Niraparib plus abiraterone acetate with prednisone in patients with metastatic castration-resistant prostate cancer and homologous recombination repair gene alterations: second interim analysis of the randomized phase III MAGNITUDE trial

BACKGROUND

Patients with metastatic castration-resistant prostate cancer (mCRPC) and BRCA alterations have poor outcomes. MAGNITUDE found patients with homologous recombination repair gene alterations (HRR+), particularly BRCA1/2, benefit from first-line therapy with niraparib plus abiraterone acetate and prednisone (AAP). Here we report longer follow-up from the second prespecified interim analysis (IA2).

PATIENTS AND METHODS

Patients with mCRPC were prospectively identified as HRR+ with/without BRCA1/2 alterations and randomized 1 : 1 to niraparib (200 mg orally) plus AAP (1000 mg/10 mg orally) or placebo plus AAP. At IA2, secondary endpoints [time to symptomatic progression, time to initiation of cytotoxic chemotherapy, overall survival (OS)] were assessed.

RESULTS

Overall, 212 HRR+ patients received niraparib plus AAP (BRCA1/2 subgroup, n = 113). At IA2 with 24.8 months of median follow-up in the BRCA1/2 subgroup, niraparib plus AAP significantly prolonged radiographic progression-free survival {rPFS; blinded independent central review; median rPFS 19.5 versus 10.9 months; hazard ratio (HR) = 0.55 [95% confidence interval (CI) 0.39-0.78]; nominal P = 0.0007} consistent with the first prespecified interim analysis. rPFS was also prolonged in the total HRR+ population [HR = 0.76 (95% CI 0.60-0.97); nominal P = 0.0280; median follow-up 26.8 months]. Improvements in time to symptomatic progression and time to initiation of cytotoxic chemotherapy were observed with niraparib plus AAP. In the BRCA1/2 subgroup, the analysis of OS with niraparib plus AAP demonstrated an HR of 0.88 (95% CI 0.58-1.34; nominal P = 0.5505); the prespecified inverse probability censoring weighting analysis of OS, accounting for imbalances in subsequent use of poly adenosine diphosphate-ribose polymerase inhibitors and other life-prolonging therapies, demonstrated an HR of 0.54 (95% CI 0.33-0.90; nominal P = 0.0181). No new safety signals were observed.

CONCLUSIONS

MAGNITUDE, enrolling the largest BRCA1/2 cohort in first-line mCRPC to date, demonstrated improved rPFS and other clinically relevant outcomes with niraparib plus AAP in patients with BRCA1/2-altered mCRPC, emphasizing the importance of identifying this molecular subset of patients.

Association of biomarkers and outcomes in patients (pts) with metastatic urothelial carcinoma (mUC) treated with immune checkpoint inhibitors (ICIs)

532

Background: ICIs form the backbone of treatment for mUC. However, only a minority of pts benefit and additional biomarkers of ICI response are needed. Methods: In our institution, we identified mUC pts treated with ICI monotherapy who had next generation sequencing (NGS). Somatic alterations present in ≥10% of pts ( ARID1A, CCND1, CDKN2A, CDKN2B, ERBB2, FGF3, FGF4, FGF19, FGFR3, KDM6A, MDM2, MLL2, PIK3CA, RB1, TERTp, TP53, TSC1), as well as DNA-damage response (DDR) alterations and tumor mutational burden (TMB) were analyzed as biomarkers. These biomarkers were individually evaluated in separate multivariate models while accounting for clinical factors including age, BMI, ECOG PS, primary tumor location, histology, hemoglobin, neutrophil to lymphocyte ratio and albumin. Multivariate cox regression and logistic regression models were used to measure hazard ratios (HR) and odds ratios (OR) for overall survival (OS), progression-free survival (PFS) and observed response rate (ORR). Results: Among 152 mUC ICI-treated pts, 107 had NGS data (FoundationOne, UCSF500, Strata), including 85 with TMB data. For the 107 pts with NGS, median age was 70 yrs, majority were male (69, 64%), Caucasian (70, 65%), had pure urothelial histology (57, 53%), and had first-line ICI (55, 51%). ORR was 35%, median PFS was 3.9 mos (95% CI: 2.6-7.5 mos), and median OS was 17.4 mos (95% CI: 14.1-30.6 mos). Biomarkers associated with improved outcomes to ICI, independent of relevant clinical factors, included alterations in ARID1A and DDR, as well as high TMB (>10 Mut/Mb). Inferior outcomes were seen in pts with CDKN2B, KDM6A, FGF3, FGF4, and FGF19 alterations (Table). Conclusions: In this large retrospective multivariate analysis controlling for clinical factors in ICI-treated mUC pts, we found multiple biomarkers associated with improved or inferior outcomes. These hypothesis-generating findings can inform clinical decision making and trial design for mUC pts treated with ICIs, and should be validated in larger cohorts. [Table: see text]

Impact of run-in treatment with abiraterone acetate and prednisone (AAP) in the MAGNITUDE study of niraparib (NIRA) and AAP in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and homologous recombination repair (HRR) gene alterations

172

Background: NIRA/AAP significantly improved outcomes in pts with mCRPC and HRR gene alterations, particularly in BRCA, in the phase 3 MAGNITUDE study. As a practical measure, pts were permitted to receive up to 4 mos of AAP (in 1L mCRPC) prior to randomization to allow time for genomic testing. We evaluated the impact of AAP run-in treatment on the efficacy of NIRA/AAP. Methods: 423 pts with mCRPC and HRR gene alterations were randomized 1:1 to receive NIRA/AAP or placebo (PBO)/AAP. At the prespecified second interim analysis, a sensitivity analysis based on the duration of AAP run-in was conducted. Pts with BRCA alterations were also analyzed separately. Results: Median duration of prior AAP treatment received was 1.9 (range, 0.3–4.1) mos. Pts receiving AAP ≤2 mos had similar benefit (radiographic progression-free survival [rPFS] hazard ratio [HR], 0.69 [95% confidence interval [CI], 0.36-1.30]; time to cytotoxic chemotherapy [TCC] HR, 0.52 [95% CI, 0.24-1.11]; time to symptomatic progression [TSP] HR, 0.32 [95% CI, 0.13-0.79]; Table) to pts not receiving any prior AAP. rPFS benefit was not demonstrated in pts who had previously received AAP >2 – 4 mos: HR, 1.47 (95% CI, 0.66-3.30). Findings were consistent in the BRCA population. Conclusions: Pts receiving a short run-in (≤2 mos) of AAP alone obtained similar benefit from NIRA/AAP as those who received both NIRA/AAP together for initial treatment of mCRPC. While interpretation of data is limited by the small sample size and event numbers, for pts where NIRA/AAP is being considered as therapy, AAP may be initiated during HRR testing and combination treatment should be initiated expeditiously once HRR positivity is established to attain maximal treatment benefit. Clinical trial information: NCT03748641 . [Table: see text]

Niraparib (NIRA) with abiraterone acetate and prednisone (AAP) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and homologous recombination repair (HRR) gene alterations: Second interim analysis (IA2) of MAGNITUDE

170

Background: In the primary analysis of the phase 3 MAGNITUDE study, NIRA/AAP significantly improved outcomes in pts with mCRPC and HRR gene alterations. Here, we report results from IA2 of secondary endpoints in MAGNITUDE. Methods: 423 eligible pts with mCRPC and HRR alterations (HRR+ cohort) were randomized 1:1 to receive NIRA/AAP (n = 212) or placebo (PBO)/AAP (n = 211). At the prespecified IA2, secondary endpoints (time to cytotoxic chemotherapy [TCC], time to symptomatic progression [TSP], overall survival [OS]) were formally assessed and the primary rPFS endpoint was updated in the HRR+ cohort, with sensitivity analysis performed for the subgroup of pts with BRCA alterations. Results: Updated descriptive rPFS results at IA2 (cutoff: June 17, 2022) were consistent with the primary analysis in the HRR+ cohort. In the BRCA subgroup, NIRA/AAP extended median rPFS to 19.5 mos vs 10.9 mos with PBO/AAP. NIRA/AAP led to statistically significant benefit in TSP in the HRR+ cohort with consistent benefit in the BRCA subgroup. Continued consistent improvement of TCC was seen with NIRA/AAP in the HRR+ cohort and in the BRCA subgroup. There was a trend towards improved OS with NIRA/AAP in the BRCA subgroup in the primary stratified analysis and the multivariate analysis (MVA), accounting for imbalances in key baseline characteristics. BRCA pts treated with NIRA/AAP experienced delayed time to worst pain intensity (HR, 0.70; 95% CI, 0.44, 1.12; nominal P = 0.1338) and pain interference (HR, 0.67; 95% CI, 0.40, 1.12; nominal P = 0.1275) compared to PBO/AAP. The safety profile at IA2 was consistent with that of the primary analysis, with no new safety signals observed. Conclusions: With 26.8 months of median follow-up, there was a statistically significant and meaningful clinical benefit in TSP and meaningful clinical benefit in TCC. Additionally, updated rPFS results from MAGNITUDE IA2 were consistent with the primary analysis; OS benefit was not conclusive due to immaturity and will be followed through to final analysis. Taken together, these data continue to support the use of NIRA/AAP in pts with mCRPC and BRCA alterations or select other HRR gene alterations. Clinical trial information: NCT03748641 . [Table: see text]

Disparities in germline testing by race/ethnicity and preferred language in patients with prostate cancer

112

Background: A remote Genetic Testing Station (GTS) workflow was implemented at an academic medical institution to expand access to genetic testing for patients with prostate cancer. During a telephone appointment, a genetic counselor assistant collects family history and facilitates genetics education, research consent, and remote sample collection for multi-gene panel testing. We compared testing completion and patient loss from workflow based on race/ethnicity and preferred language to identify disparities. Methods: Metrics were collected prospectively and analyzed retrospectively for patients with metastatic or high-grade prostate cancer referred to genetics between 3/15/2020 – 6/30/2022. Self-reported race, ethnicity, and preferred language were collected by chart review. Testing completion was compared between groups using Fisher’s exact test, with White non-Hispanic (WNH) and Preferred Language English (PLE) cohorts as controls. Odds ratios and 95% confidence intervals were reported. Patient loss at workflow checkpoints (scheduling, consenting, sample collection, and results release) was summarized for each group. Results: 827 eligible patients were identified: 78 (9%) Asian /Pacific Islander (API), 51 (6%) Black non-Hispanic (BNH), 42 (5%) Hispanic, and 625 (76%) WNH. 31 patients reporting other non-Hispanic race were not included in the analysis. 30 patients (4%) self-reported Preferred Language non-English (PLNE) and 797 (96%) PLE. BNH patients were significantly less likely to complete testing compared to WNH patients (OR 0.320, 95%CI: 0.168, 0.632, p<0.001). There was no difference in testing completion in API (OR 0.918, 95%CI: 0.467, 1.944, p=0.797) or Hispanic (OR 0.743, 95%CI: 0.325, 1.918, p=0.466) compared to WNH patients. PLNE were significantly less likely to complete testing (OR 0.393, 95%CI: 0.171, 0.965, p=0.016) compared to PLE patients. Patient loss occurred primarily at consenting and sample collection. 14% of BNH, and 9% of Hispanic patients did not consent, compared to 4% of WNH. 17% of PLNE did not consent compared to 5% of PLE patients. 13% of BNH did not return a sample, compared to 3% of WNH patients. Conclusions: In remote GTS, BNH and PLNE patients were significantly less likely to complete germline testing than WNH and PLE patients respectively. Disparities in patient loss were most pronounced at consenting and sample collection. Measures to mitigate disparities include assisted consenting (with interpreter as needed) and video-assisted or in-clinic sample collection. [Table: see text]

Efficacy of subsequent treatments in patients who progressed to mCRPC following treatment with apalutamide for nonmetastatic castration-resistant prostate cancer (nmCRPC): A post-hoc analysis of the SPARTAN phase III trial

157

Background: Apalutamide (Apa) delays the onset of metastases and extends survival in nmCRPC. However, the benefit of subsequent therapy for metastatic castration resistant prostate cancer (mCRPC) following progression on Apa remains inadequately explored. Methods: A post-hoc analysis of SPARTAN, a randomized phase III (NCT01946204), double-blind, placebo-controlled trial with Apa for the treatment of men with nmCRPC was undertaken in order to assess the impact of post-protocol treatment. Patients included in this analysis were SPARTAN patients who developed mCRPC while on Apa and received a first subsequent therapy for mCRPC (the “Next Cohort”). The index date of the analysis was the initiation of first subsequent treatment for mCRPC. The baseline characteristics of the Next Cohort (reported from the time of initial randomization because updated characteristics at the index date could not be derived) were compared to those of the ITT Apa arm in SPARTAN. Subsequent overall survival (sOS) and subsequent progression-free survival per physician assessment (sPFS) were calculated from the index date using Kaplan-Meier method. Results: At study completion, 237 patients remained on Apa without progression, while 311 were included in the Next Cohort. Of these, 241 (77.5%) received abiraterone acetate plus prednisone (AAP) provided by the sponsor as an option as first subsequent treatment, 29 (9.3%) received docetaxel; 20 (6.4%) enzalutamide and 21 other treatments (6.8%). Compared to the ITT Apa arm in SPARTAN, a higher proportion of the Next Cohort had PSA doubling time ≤6 months (79.1% vs 71.5%) and a PSA value above median at baseline, and experienced poorer PSA response (51% PSA90 overall response rate vs 62%) whilst on apalutamide treatment. The median sPFS and sOS were 6.8 months (95% confidence interval, CI, 5.8-7.9) and 20.0 months (95% CI, 17.0-22.6), respectively. Choice of subsequent next treatment did not appear to have an impact on sPFS and sOS. Conclusions: Limitations of this analysis include its retrospective nature and the lack of randomization to first line mCRPC therapy and related potential confounding, and the inclusion of patients who had progressed at SPARTAN study completion with associated poorer prognosis. Nevertheless, the analysis suggests comparable efficacy of selected first line mCRPC therapies, following progression on Apa for nmCRPC. Clinical trial information: NCT01946204 . [Table: see text]

Association of biomarkers and response to immune checkpoint inhibitors (ICIs) in patients with metastatic urothelial carcinoma (mUC) with high and low tumor mutation burden (TMB)

534

Background: ICIs are frequently used as therapy in mUC, but only a minority of patients (pts) respond to treatment. High TMB is associated with improved outcomes to ICIs. However, much is unknown about biomarkers associated with ICI outcomes in pts with high and low TMB respectively. Methods: We retrospectively identified mUC pts with known TMB status and available next generation sequencing (NGS) results treated with ICI monotherapy at our institution. TMB high was defined as ≥ 10 mutations/Mb, with the rest being TMB low. Somatic alterations present in ≥10% pts ( ARID1A, CCND1, CDKN2A, CDKN2B, ERBB2, FGF3, FGF4, FGF19, FGFR3, KDM6A, MDM2, MLL2, PIK3CA, RB1, TERTp, TP53, TSC1), and presence of DNA damage response (DDR) alterations were assessed as biomarkers of interest. Within the TMB-high and TMB-low pt groups we separately assessed patients based on the presence or absence of these somatic alterations, APOBEC mutational signature and high PD-L1 expression. Log rank test was used to determine differences in overall survival (OS) and progression free survival (PFS) among these groups. P-value ≤0.05 was considered significant. Results: Among 107 mUC pts treated with ICI monotherapy between 12/2014 and 3/2022 who had NGS data (UCSF500, FoundationOne, Strata), 85 pts had TMB data, including 47 TMB high pts and 38 TMB low pts. Among 85 pts with known TMB status, median age was 76 yrs, the majority were male (55, 65%), Caucasian (57, 67%), had pure urothelial histology (46, 55%) and were treated with ICIs in frontline setting (47, 55%). Median OS was 17.2 mos and median PFS was 3.42 mos. In TMB high pts, presence of DDR , MLL2, KDM6A, PIK3CA and TERTp alterations were each associated with improved outcomes, while presence of CDKN2B alterations was associated with inferior outcomes (Table). Among TMB low pts, those with RB1 alterations had shorter mOS (11.3 months vs 17.2 months; p=0.04) compared to wild-type pts. Conclusions: In this single-center retrospective analysis of mUC pts, we identified somatic alterations that were predictive of outcomes with ICI treatment in TMB high and TMB low pts respectively. Further exploration of biomarkers in patients stratified by TMB status is warranted in larger cohorts. [Table: see text]

Reliability of real-world data for diagnosis of metastatic prostate cancer

397

Background: Real-world data (RWD) is playing an increasingly important role in cancer research. Surrogate endpoints such as metastasis-free survival play an important role in prostate cancer research, leading to interest in its computational extraction, typically with use of International Classification of Disease (ICD) metastatic codes. While prior studies have suggested that ICD codes are valid for identification of patients (pts) with metastatic prostate cancer (MPC), delays in coding may impact their accuracy. The objective of this informatics-based study is to quantify the time delay between diagnosis of MPC and entry of ICD MPC-related code and its interaction with changing institutional healthcare processes. Methods: A single institutional EHR data warehouse was queried to identify a random sample of 100 pts with MPC diagnosis based on ICD codes (ICD10 C79 or ICD9 198.5) from 2013-2021 who were also seen in the genitourinary medical oncology program (GUMOP). Of note, in 6/2018, the GUMOP adopted EHR-specific MPC visit diagnosis identifiers (Dx ID) to improve MPC coding during clinic independent of ICD codes typically used by RWD researchers. Thus, the study cohort was designed to include pts whose first follow up after being diagnosed with MPC was before (n = 50) or after (n = 50) Dx ID implementation. Date of first MPC ICD code entry at any point in the EHR was compared against true date of MPC, based on physician review of definitive imaging or pathology. Data analysis was performed with Wilcox Signed rank test, bivariate analyses, and multivariable linear regression. Covariates included modality of diagnosis confirmation and timing with Dx ID implementation. Results: One hundred pts with MPC ICD coded in the EHR were included, with 29 pts diagnosed by PSMA PET and 71 by conventional imaging. Median time from true MPC diagnosis to first subsequent clinic follow up was < 1 month (IQR 0-2), while median time from true MPC diagnosis to entry of ICD MPC-related code was longer at 4mo (IQR 0-15). 5 pts had C79 applied for N1 disease and 10 pts for work-up of biochemical recurrence. On multivariable analysis of potential factors affecting time interval to MPC ICD entry, Dx ID implementation (b = -6.5 mo [95% CI -1.8 to -11.2], p = 0.007) and non-PSMA based diagnosis (b = -5.7 mo [95% CI -0.5 to -10.8], p = 0.03) were independently associated with shorter time to ICD coding. In subset analysis of the cohort after Dx ID implementation, use of both ICD and Dx ID to identify pts with MPC reduced the median time from true MPC diagnosis to EHR coding (1mo, IQR 0-6.3) compared to ICD alone (2mo, IQR 0-8) (p = 0.003). Conclusions: Timing of MPC ICD entry is highly variable and may carry biases derived from healthcare processes, including data entry and diagnostic testing. This may be improved with EHR workflow interventions. It is essential to have domain knowledge of clinical coding practices to improve information retrieval and recognize potential limitations and biases.

Health-related quality of life (HRQoL) and pain in the MAGNITUDE study of niraparib (NIRA) with abiraterone acetate and prednisone (AAP) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and homologous recombination repair (HRR) gene alterations

5060

Background: Results from the international, randomized, double-blind, phase 3 MAGNITUDE study demonstrated that NIRA + AAP improved radiographic progression-free survival, time to cytotoxic chemotherapy, and time to symptomatic progression, with manageable toxicity in pts with mCRPC and HRR alterations (9-gene panel). Here, we report HRQoL and pain in MAGNITUDE. Methods: Eligible pts with mCRPC and HRR alterations were randomized 1:1 to NIRA + AAP or placebo (PBO) + AAP orally daily in 28-day cycles. Pts had ECOG status ≤1 and a Brief Pain Inventory–Short Form (BPI-SF) worst pain score ≤3 in prescreening. HRQoL assessments on day 1 of specified cycles included Functional Assessment of Cancer Therapy–Prostate (FACT-P) and BPI-SF. Changes from baseline were compared between treatment arms using repeated measures analysis. Proportional hazards regression models were used to compare time to deterioration (TTD) in worst pain intensity between arms. Results: Compliance for FACT-P and BPI-SF was > 80%. Most pts maintained low pain levels over time. Repeated measures analyses showed no clinically meaningful differences in pain over time or between arms. Median TTD in pain intensity was not reached in either arm. At the 25th percentile, there was a trend toward longer TTD in pain intensity with NIRA + AAP vs PBO + AAP (11.1 vs 10.1 mo; HR, 0.87; 95% CI, 0.61-1.24). HRQoL was maintained with NIRA + AAP, with no clinically meaningful differences in FACT-P total score over time or between arms. There was a trend toward greater worsening in early cycles on FACT-P physical wellbeing with NIRA + AAP vs PBO + AAP, driven by events within the known safety profile of NIRA + AAP (worsening of side effect bother, lack of energy, and nausea); however, overall, most pts reported minimal side effect burden (Table). Conclusions: In MAGNITUDE, most pts maintained low pain levels and positive HRQoL over time, with no clinically meaningful differences between treatment arms, further supporting the use of NIRA + AAP in pts with mCRPC and HRR alterations. Side effect burden was perceived as low in both arms. Although more pts on NIRA+AAP reported worsening side effects, the symptoms were generally perceived as mild. Clinical trial information: NCT03748641. [Table: see text]

Phase 1a/1b study of FOR46, an antibody drug conjugate (ADC), targeting CD46 in metastatic castration-resistant prostate cancer (mCRPC)

3001

Background: FOR46, a fully human antibody (ab) conjugated to monomethyl auristatin E (MMAE), targets a tumor selective epitope of CD46, which is highly expressed in mCRPC and treatment-emergent small cell neuroendocrine cancer (t-SCNC). CD46 is enriched in tumor cells upon treatment with androgen signaling inhibitors (ASI). Following dose escalation (Phase 1a), dose expansion was undertaken in 2 cohorts (Phase 1b): 1) Pts with de novo or t-SCNC and 2) pts with mCRPC without a t-SCNC component. Pts with adenocarcinoma enrolled in dose escalation and expansion are included in this analysis. Methods: Eligible pts had mCRPC, with progression on at least 1 ASI, with no prior chemotherapy for CRPC. Phase 1a pts received FOR46 0.1-3.0 mg/kg IV Q3 weeks (wks). The primary objectives in phase 1a were to assess adverse effects (AEs) and select the phase 1b dose; and in phase 1b to assess efficacy. For phase 1b, tumor biopsy in the CRPC setting for assignment to the 2 cohorts was required. CD46 expression was not required for inclusion in the expansion cohort, but was evaluated using a non-epitope specific CD46 polyclonal ab. Histology and CD46 expression were centrally reviewed. Results: Thirty-three pts were enrolled in phase 1a and 10 in phase 1b (including 6 treated in ph1a at the expansion dose or higher). Overall, 36 pts were treated at doses > 1.2 mg/kg. Following excess toxicity in pts with body mass indices > 30 (3 of 3 with Gr 4 neutropenia and 1 of 3 with Gr 3 fatigue at 2.4 mg/kg), further dosing was calculated using adjusted body weight (AJBW) rather than actual weight, allowing escalation to 3.0 mg/kg. The 2.7 mg/kg dose by AJBW was determined to be the MTD and phase 1b dose. The most common AEs at the 2.7 mg/kg dose were neutropenia (77% Gr 3 or 4), infusion reactions (37%, all < Gr 2), fatigue (31%, all < Gr 2) and peripheral neuropathy (24%, all < Gr 2)). Fourteen of 31 evaluable pts (45.2%) at > 1.2 mg/kg achieved a PSA50 response with 10 (32.3%) confirmed. Five pts were not evaluable for PSA response; 3 had no post-baseline PSA and 2 had baseline PSA < 1 ng/mL. The median duration of confirmed PSA50 response is >16 wks (range 6-48+ wks, with 4 ongoing at 12, 24, 25 and 48 wks). 18 pts had measurable lesions; 8 of 18 (44.4%) had tumor regression, with 4 (22.2%) confirmed partial responses (PR). The median duration of response is > 14 wks (range 9 -31+ weeks with 2 ongoing at 13 and 31 wks). Eight pts were evaluable for CD46 expression with a median H-score of 245 (range 0-300). Two pts with PRs had H-scores of 15 and 300; 4 with confirmed PSA50 had H-scores of 10, 15, 40 and 300. Conclusions: FOR46, a novel ADC targeting CD46, demonstrates clinical activity in mCRPC pts, with an acceptable safety profile, similar to other MMAE-containing ADCs. FOR46 merits further investigation in pts with mCRPC, alone and in combination with agents that enhance CD46 expression. Clinical trial information: NCT03575819.

Transcriptional profiling of matched biopsies reveals molecular determinants of enzalutamide resistance

5058

Background: Castration-resistant prostate cancer (CRPC) is the lethal form of the disease. One of the principal therapies in CRPC is the potent androgen receptor (AR) signaling inhibitor enzalutamide (enza). Most patients benefit from enza, but disease progression is nearly universal. A variety of resistance mechanisms have been described by comparing enza-naïve and enza-resistant tumors. However, these results are largely from different groups of patients and do not provide information on the changes induced by enza within a given patient. Lineage plasticity—most commonly-exemplified by loss of AR signaling and switch from a luminal to an alternate differentiation program—is a particularly aggressive resistance mechanism. Importantly, lineage plasticity appears to be increasing in incidence since more widespread use of potent AR signaling inhibitors such as enza. To improve our understanding of resistance mechanisms induced by enza treatment, we analyzed the transcriptomes of matched metastatic CRPC patient biopsies obtained prior to treatment and at the time of disease progression. Methods: All biopsies were obtained as part of the Stand Up 2 Cancer/Prostate Cancer Foundation-funded West Coast Dream Team, a prospective, IRB-approved protocol focused on understanding the biology of metastatic CRPC. We identified 21 patients for whom matched tumor biopsies with RNA-seq were available prior to starting treatment with enza and at the time of progression while still taking enza. Results: Our RNA-seq analysis demonstrates that the majority of progression tumors cluster with their baseline pair, suggesting that enza does not markedly change the tumor transcriptome in most cases. Three of 21 patients showed evidence of lineage plasticity at progression by gene expression analysis. By analyzing the RNA-seq data, we identified pathways linked to stemness that were more activated in baseline tumors from patients whose progression tumors underwent lineage plasticity. Furthermore, we identified a gene signature enriched in these baseline tumors that was associated with risk of lineage plasticity after enza treatment. We determined that high expression of this signature was strongly associated with poor survival from the time of AR signaling inhibitor treatment in independent patient samples, suggesting this signature is linked to poor patient outcome. Conclusions: Enza-resistant tumors are heterogeneous. Most tumors do not undergo significant transcriptional changes at progression vs. baseline. Matching recent reports, approximately 15% of tumors underwent lineage plasticity upon progression. Our work implicates a gene program that may predispose tumors to enza-induced lineage plasticity. Finally, the gene signature we identified may be a marker of lineage plasticity risk and tumor aggressiveness in CRPC prior to the initiation of AR signaling inhibitor therapy.

Gene-by-gene analysis in the MAGNITUDE study of niraparib (NIRA) with abiraterone acetate and prednisone (AAP) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and homologous recombination repair (HRR) gene alterations

5020

Background: NIRA + AAP significantly improved outcomes in pts with mCRPC and HRR gene alterations in the Phase 3 MAGNTUDE study. There is a paucity of data supporting use of PARP inhibitors in pts with HRR gene alterations other than BRCA1/2. We report on the efficacy of NIRA + AAP in pts with mCRPC and a qualifying single gene HRR alteration other than BRCA1/2. Methods: A pre-specified analysis was undertaken of the primary endpoint (radiographic progression-free survival [rPFS] by BICR), secondary endpoints (time to cytotoxic chemotherapy [TCC], time to symptomatic progression [TSP], overall survival [OS]), as well as time to PSA progression (TPSA) and overall response rate (ORR) across 186 pts (91 randomized to NIRA + AAP, 95 to PBO + AAP) with an alteration in the ATM, BRIP1, CDK12, CHEK2, FANCA, HDAC2, or PALB2 gene (excluding cooccurring alterations) . This analysis of individual alterations was not powered for formal statistical inference. Given the rarity of some alterations, groups based on functional similarity are also presented. Results: (Table). Pts with PALB2 or CHEK2 alterations had consistent improvement across all endpoints. In pts with ATM alterations benefit was observed in TCC, TSP, TPSA and ORR. There was benefit only in TPSA and ORR for pts with CDK12 alterations. When combined into functional groups, pts with an alteration in the HRR-Fanconi pathway ( BRIP1, FANCA, and PALB2) as well as pts with a HRR associated alteration ( CHEK2 or HDAC2) showed improvement in all endpoints. Conclusions: These data support the overall conclusions of the MAGNITUDE primary analysis and support benefit of NIRA + AAP in pts with HRR mutations beyond BRCA1/2. Clinical trial information: NCT03748641. [Table: see text]

Biomarkers predictive of response to enfortumab vedotin (EV) treatment in advanced urothelial cancer (aUC)

531

Background: EV is an antibody-drug conjugate which recently received full FDA approval for treatment-refractory aUC. Molecular biomarkers and characteristics of patients (pts) most likely to respond to EV therapy have not been well defined. Methods: We retrospectively identified all aUC pts treated with EV at our institution. Clinicopathologic, treatment and response data were abstracted from pt charts. Pts were considered responders to EV if they had a complete response on initial scans after 2-3 months of treatment, or were treated with EV for ≥ 6 months. Responders and non-responders were compared in terms of their molecular and clinical characteristics using Chi-squared test. Most common somatic alterations present in ≥10 pts ( TERTp, TP53, CDKN2A, CDKN2B) were also used to divide pts with available next-generation sequencing (NGS) results into groups with and without these alterations. Log rank test was used to determine differences in overall survival (OS) and progression free survival (PFS) among these groups. Results: Between 1/2020 and 8/2021 a total of 32 pts received EV and 28 had NGS data available with either FoundationOne (14 pts), UCSF500 (13 pts) or Strata (1). Median age was 69.5 years, 24 (75%) were male, 22 (69%) Caucasian, 22 (69%) had pure urothelial histology and 22 (69%) primary tumor location in the bladder. At EV start, 24 (75%) had visceral metastases (mets), 8 (25%) had liver mets, and 13 (41%) had bone mets. Median follow-up from EV start was 12.5 months (range 0.5-36); 20 (63%) pts received EV monotherapy, and 12 (37%) received EV as part of a combination regimen. Non-responders were more likely to have bone metastases (69% vs 21%, p<0.01), but were otherwise similar in baseline clinical characteristics to responders. TP53 alterations were enriched in responders relative to non-responders, whereas non-responders had more CDKN2B alterations (Table). Similar findings were seen in the subset of pts treated with EV monotherapy. Pts with TP53 alterations had longer OS (NR vs 17.0 months, p=0.06) and PFS (NR vs 6.6 months, p=0.04) relative to wild-type pts. Shorter PFS was seen in pts with CDKN2A (4.4 months vs NR, p=0.05) and CDKN2B (4.3 months vs NR, p=0.02) alterations, but no differences in OS were observed. Conclusions: In this retrospective cohort of aUC pts with available NGS data, presence of TP53 and absence of CDKN2A and CDKN2B alterations were associated with favorable responses and improved clinical outcomes with EV, suggesting they may be biomarkers of response to EV. These preliminary findings should be validated in larger cohorts.[Table: see text]

Phase 3 MAGNITUDE study: First results of niraparib (NIRA) with abiraterone acetate and prednisone (AAP) as first-line therapy in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) with and without homologous recombination repair (HRR) gene alterations

12

Background: Approximately 20% of mCRPC has alterations in genes associated with HRR and is responsive to PARP inhibitors (PARPi) such as NIRA. Combined PARPi with androgen receptor pathway targeting may also benefit unselected mCRPC. MAGNITUDE assessed whether adding NIRA to AAP improves outcomes in pts with mCRPC with or without alterations in HRR associated genes. Methods: MAGNITUDE (NCT03748641) is a randomized, double-blind phase 3 study. In eligible mCRPC pts, ≤4 mos of prior AAP for mCRPC was allowed. Pts with (HRR biomarker [BM]+; ATM, BRCA1, BRCA2, BRIP1, CDK12, CHEK2, FANCA, HDAC2, PALB2) and without specified gene alterations (HRR BM-) were randomized 1:1 to receive NIRA 200 mg once daily + AAP or placebo (PBO) + AAP. Primary endpoint was radiographic progression-free survival (rPFS) assessed by blinded independent central review (BICR) in the BRCA1/2 group followed by all HRR BM+ pts. Secondary endpoints were time to initiation of cytotoxic chemotherapy (TTCC), time to symptomatic progression (TTSP) and overall survival (OS). Other endpoints included time to PSA progression (TTPP) and objective response rate (ORR). Results: 423 HRR BM+ pts were randomized to NIRA + AAP (n = 212) or PBO + AAP (n = 211). Median age was 69, 23% had prior AAP, 21% had visceral metastases, and 53% had BRCA1/2 mutations. Median follow-up was 18.6 mos. NIRA + AAP significantly improved rPFS by BICR in the BRCA1/2 subgroup and in all HRR BM+ pts, reducing the risk of progression or death by 47% (16.6 vs 10.9 mo) and 27% (16.5 vs 13.7 mo) respectively (Table), vs PBO + AAP. Investigator assessed rPFS was consistent with BICR. NIRA + AAP delayed TTCC, TTSP, and TTPP and improved ORR in HRR BM+ pts (Table). First interim analysis of OS is immature. The preplanned futility analysis in 233 HRR BM- pts showed no benefit of adding NIRA to AAP in the prespecified composite endpoint (first of PSA progression or rPFS; HR, 1.09; 95% CI, 0.75-1.57). No new safety signals were seen. In HRR BM+ pts, 67% and 46.4% had grade 3/4 AEs and 9% and 3.8% discontinued treatment in the NIRA + AAP and PBO + AAP arms, respectively. There were no clinically significant differences in overall quality of life (FACT-P). Conclusions: NIRA + AAP improves rPFS and other clinically relevant outcomes in pts with mCRPC and alterations in HRR associated genes. There was no evidence of benefit with the addition of NIRA to AAP in HRR BM- pts with mCRPC. Clinical trial information: NCT03748641. [Table: see text]

Clinical and molecular features of low prostate-specific membrane antigen (PSMA) expression in patients (pts) with metastatic castration resistant prostate cancer (mCRPC)

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Background: Low PSMA uptake on positron-emission tomography is seen in up to 30% of mCRPC pts and represents a clinically distinct subgroup with adverse outcomes. We assessed transcriptional and clinical features associated with low PSMA ( FOLH1) gene expression in mCRPC. Methods: A retrospective analysis of mCRPC biopsy samples with RNA-seq data was undertaken. Normalized FOLH1 expression was compared across histologic subtypes and sites of disease. We assessed the association between FOLH1 expression, selected androgen receptor (AR) target genes, master regulators of neuroendocrine differentiation, and previously validated AR activity and treatment-associated small cell neuroendocrine carcinoma (t-SCNC) transcriptional signature scores using Pearson correlations. Associations between FOLH1 and both PSA50 response to subsequent AR-targeted therapy and overall survival (OS) were examined by logistic regression and Cox proportional hazard models, respectively. Results: Samples from 97 pts were identified, of which 18% harbored t-SCNC histology. 45% of pts had visceral metastases at the time of biopsy, and 41% received subsequent AR-targeted therapy. Median FOLH1 expression was lower in pts with visceral metastases vs no visceral metastases (14.7 vs 15.6, p = 0.02) but was not significantly different across t-SCNC vs adenocarcinoma biopsies (14.3 vs 15.4, p = 0.13). FOLH1 expression was positively correlated with AR transcriptional activity and AR target genes, and negatively correlated with master regulators of neuroendocrine differentiation and t-SCNC transcriptional signature scores (Table). Low FOLH1 expression did not predict PSA50 response to subsequent AR-targeted therapy (OR 0.97, p = 0.8), but was associated with shorter OS on univariate analysis (HR 1.09, 95% CI 1.02-1.16, p=0.01). A post-hoc analysis revealed a trend towards decreased median OS in pts with FOLH1 expression <12 (7.5 vs 17.1 months, log-rank p = 0.06). Conclusions: In this retrospective analysis of mCRPC pts, low FOLH1 expression was associated with transcriptional features of t-SCNC, decreased AR activity, and shorter OS. These findings are hypothesis-generating and prospective validation is needed.[Table: see text]

Serial stereotactic body radiation therapy for oligometastatic prostate cancer (PCa) detected by positron emission tomography (PET) imaging

109

Background: Radiopharmaceuticals, including Ga-68-prostate specific membrane antigen (PSMA)-11, F-18-fluciclovine, and choline C-11, are increasingly used to stage and inform therapies for PCa. Stereotactic body radiation therapy (SBRT) to PET-detected oligometastatic PCa has been shown to improve progression free survival (PFS) compared to observation. However, for men who subsequently develop oligorecurrent disease, outcomes following second SBRT are unknown. Methods: A retrospective, single-center, cohort study was conducted. Pts were identified through electronic health records. Inclusion criteria included pts with oligometastatic (1-5 lesions) PCa detected on PSMA, fluciclovine, or choline C-11 PET who underwent 2 consecutive courses of SBRT to tracer-avid oligometastatic disease between 7/2013 and 7/2021. Exclusion criteria included presence of visceral metastases and pure small cell neuroendocrine PCa. Data on stage, tracer type, concurrent systemic therapy, and prostate-specific antigen (PSA) responses for first SBRT (SBRT1) and second SBRT (SBRT2) were collected. Outcomes included PSA decline of ≥50% (PSA50), ≥90% (PSA90), and PSA-PFS. SBRT2 outcomes were compared based on change of concurrent systemic therapy with SBRT2 (e.g., addition of abiraterone or anti-androgen withdrawal) and PSA50 to SBRT1 using Fisher’s exact text and Wilcoxon rank sum test, respectively. Results: A total of 12 pts met eligibility criteria. At SBRT1, 10 (83%) pts had hormone-sensitive PCa (HSPC) and 2 (17%) had castration-resistant PCa (CRPC). For PET tracers, 7 (58%) used PSMA, 4 (33%) fluciclovine, and 1 (8%) choline. After SBRT1, 12 pts (100%) had a PSA decline, 8 (67%) had a PSA50 response, and 6 (50%) a PSA90 response. Median PSA PFS after SBRT1 was 30mo (95%CI 9-65mo). Six (50%) SBRT1 pts had a concurrent change in systemic therapy. At SBRT2, 8 (67%) pts had HSPC and 4 (33%) had CRPC; 7 (58%) used PSMA and 5 (42%) fluciclovine. After SBRT2, 12 (100%) pts had a PSA decline, 8 (67%) had a PSA50 response, and 8 (67%) a PSA90 response. After SBRT2, median PSA PFS was 23mo (95%CI 12-35mo). Among 7 pts who had a concurrent change in systemic therapy with SBRT2, all (100%) had a PSA50 response; among 5 who did not (4 of whom did not receive any systemic therapy), 1 (20%) had a PSA50 response (P=0.01). Among 8 pts who had a PSA50 response to SBRT1, 7 (88%) had one to SBRT2; among 4 who did not have a PSA50 response to SBRT1, 1 (25%) had one to SBRT2 (P=0.01). No complications related to SBRT were documented. Conclusions: Serial SBRT for oligometastatic PCa detected on fluciclovine, PSMA, or choline PET is feasible and can achieve PSA declines independent of systemic therapy. PSA responses were greater when systemic therapy was changed. This preliminary evidence of benefit, based on PSA responses and PSA PFS, provides rationale for larger, prospective studies of serial SBRT for oligometastatic PCa.

HIF-pathway genes prognostic for progression-free and overall survival in metastatic clear cell renal cell carcinoma (mccRCC)

370

Background: Clear cell renal cell carcinoma (ccRCC) is characterized by defects in the Von Hippel-Lindau/hypoxia-inducible factor (VHL/HIF) pathway. Several FDA-approved RCC therapies target the products of HIF-response genes. HIF2A is a promising new target and drugs targeting HIF2A are undergoing clinical testing. A better understanding of HIF-related genes may reveal useful biomarkers and drug targets. Methods: Gene expression was determined from 324 archival pretreatment nephrectomy specimens available from the Cancer and Leukemia Group B (CALGB) 90206, a phase III trial of patients treated with INF-α vs. INF-α plus bevacizumab. TaqMan RT-qPCR was performed on the OpenArray platform using RNA extracted from tumor tissue macrodissected based on review of H&E staining by a genitourinary pathologist. HIF pathway genes were assessed across both treatment arms, utilizing the proportional hazards model as predictors of OS and PFS, with time from randomization to death or disease progression as endpoints. Results: A total of 28 HIF-related genes (involved either in canonical or non-canonical HIF regulation) were assessed in univariate PH. Nine of these genes were associated with OS (i.e., HIF2A , VEGFC, VEGFD, TGFA, VHL, CCND1, EGFR, EGLN3 and HSP90AA1); and 6 of them were also associated with PFS (i.e., HIF2A , TGFA, VHL, CCND1 and EGLN3, and HSP90AA1). The HIF isotypes HIF1A and HIF3A were not prognostic, likewise VEGFA and VEGFB. Prolyl hydroxylase domain (PHD) proteins efficiently hydroxylate HIFα in normoxic conditions. PHD isotypes EGLN (1-3) were evaluated and only EGLN3 was associated with OS and PFS. HIF is also regulated by non-canonical pathways that function independent of oxygen concentration. HSP90AA1 was the only non-canonical pathway gene that was prognostic, and it predicted both OS and PFS. When the 9 genes that were prognostic in univariate analysis were used in a backward stepwise multivariate cox regression, VEGFD, TGFA and EGLN3 predicted OS while HIF2A, VHL and TGFA predicted PFS. Conclusions: VHL, HIF2A (but not HIF1A and HIF3A), EGLN3 (but not EGLN1 and EGLN2) and some of the HIF-response genes were prognostic of both OS and PFS. HSP90AA1 was prognostic for OS and PFS, suggesting that the non-canonical HIF pathway also plays a role in disease progression. Future studies should consider these HIF pathway genes as potential drug targets, and as predictors of response to treatments targeting the hypoxia pathway and angiogenesis.[Table: see text]

Association between patient-reported outcomes (PROs) and changes in prostate-specific antigen (PSA) in patients (pts) with advanced prostate cancer treated with apalutamide (APA) in the SPARTAN and TITAN studies

73

Background: In phase 3 placebo (PBO)-controlled studies, addition of APA to androgen deprivation therapy (ADT) improved overall survival, resulted in rapid and deep PSA declines, and reduced risk of disease progression while preserving health-related quality of life (HRQoL) in nonmetastatic castration-resistant prostate cancer (nmCRPC; SPARTAN) and metastatic castration-sensitive prostate cancer (mCSPC; TITAN). This post hoc analysis evaluated the association of a deep PSA decline with PROs in these studies. Methods: Pts on ADT were randomized to APA (240 mg QD) or PBO: SPARTAN 2:1 (N = 1,207; APA n = 806), TITAN 1:1 (N = 1,052; APA n = 525). Each cycle was 28 d. PROs were assessed using Functional Assessment of Cancer Therapy-Prostate (FACT-P), Brief Pain Inventory-Short Form (BPI-SF; TITAN only), and Brief Fatigue Inventory (BFI; TITAN only) at baseline, specific cycles during study treatment, and post progression up to 1 yr. A landmark analysis at Month 3 evaluated association between deep PSA decline (≤ 0.2 ng/mL) and time to subsequent deterioration in PROs (defined as decrease ≥ 10 points FACT-P total, ≥ 3 points Physical Wellbeing, ≥ 30% baseline for BPI-SF worst pain, or ≥ 2 points for BFI worst fatigue). At time of the landmark analysis, only pts continuing treatment were included; all deep PSA responses after, and all PRO deterioration events before, were ignored. Time-to-event end points were analyzed by Kaplan-Meier method and Cox proportional hazards model. Results: Median treatment durations were 32.9 mo (SPARTAN) and 39.3 mo (TITAN). Per assessment, > 90% (SPARTAN, cycles 1-81) and > 50% (TITAN, cycles 1-33) of eligible pts completed FACT-P; BPI-SF and BFI, both > 62% (TITAN, cycles 1-33). Pts in either study who achieved PSA ≤ 0.2 ng/mL at Month 3 had a lower risk of deterioration in FACT-P total or Physical Wellbeing (Table). Pts in TITAN with PSA ≤ 0.2 ng/mL at Month 3 had a lower risk of BPI-SF worst pain intensity or BFI worst fatigue intensity progression (Table). Conclusions: Deep and rapid PSA responses with APA were associated with prolonged time to deterioration in HRQoL, FACT-P Physical Wellbeing, BPI-SF worst pain intensity, and BFI worst fatigue intensity in pts with advanced PC. Clinical trial information: NCT02489318 (TITAN); NCT01946204 (SPARTAN). [Table: see text]

Evaluating changes in “good safety monitoring” for cancer clinical trial participants during the COVID-19 pandemic

217

Background: Comprehensive and frequent safety monitoring is an essential component of clinical trial conduct to accurately characterize potential toxicities of a study drug and to minimize potential harm to study participants. The COVID-19 pandemic substantially impacted the delivery of cancer care with reduced frequency of overall and in-person visits. We hypothesized that reporting of serious adverse events (SAEs) occurring on clinical trials may have been impacted by these care delivery changes. The current study evaluated pandemic-related changes in the frequency of safety monitoring for cancer patients (pts) enrolled on a clinical trial and identified predictors of SAE reporting before and during the pandemic. Methods: This study included all adult cancer pts enrolled in interventional therapeutic clinical trials at an academic cancer center between 1/1/2019 and 12/30/2020. In this analysis, the "pre-pandemic" period was defined as the time between 1/1/19 and 3/14/20, and the pandemic period between 3/15/20 and the data cutoff date of 12/30/2020. SAE was defined as a grade 3 or grade 4 adverse event (AE) as reported by the trial. Demographic characteristics of pts, visit type (virtual vs in-person), and frequency of SAE reporting were summarized pre-pandemic and during the pandemic. A multivariate logistic regression model was employed to identify predictors of SAE reporting, with the outcome defined as report of at least one SAE from the time pts went on study until the data cutoff date. Covariates included age, gender, race (white vs. non-white), having at least one virtual visit, and enrollment on a trial before versus during the pandemic. Results: This study included 190 pts; 138 (73%) enrolled on trial pre-pandemic and 52 (27%) enrolled during the pandemic. During-pandemic participants were more likely to be older than pts enrolled pre-pandemic, but otherwise the groups were similar in terms of race and gender. Overall, 78 pts (41%) reported an SAE. Among pre-pandemic enrollees, 50% reported at least one SAE, compared to 17% among during-pandemic enrollees. In the multivariate logistic regression model, only enrolling on trial pre-pandemic was associated with a higher likelihood of reporting at least one SAE. Visit type (virtual vs. in-person) was not recorded in over half of during-pandemic patient encounters. Conclusions: There was a significant decline in frequency of SAE reporting during the COVID-19 pandemic. While having at least one virtual visit was not a significant predictor of SAE reporting in the multivariate regression model, our analysis may underrepresent the association of virtual visits and SAE reporting. As the number of virtual visits is expected to stay high post-pandemic, further work is needed to characterize the association of virtual visits and SAE reporting to ensure ongoing adequate safety monitoring for clinical trial patients.

A phase (Ph) 1b/2 study of ribociclib (R) in combination with docetaxel (D) plus prednisone (P) in metastatic castration-resistant prostate cancer (mCRPC)

5043

Background: The survival benefit of D in mCRPC is modest. CDK4/6 inhibitors such as R have shown synergistic activity with taxanes in pre-clinical cancer models. We sought to determine the safety and efficacy of R + D + P in mCRPC patients (pts). Methods: This was a Ph 1b/2 multicenter, open-label single arm trial of mCRPC pts with progression (PD) on ≥ 1 prior androgen receptor signaling inhibitor (ARSi) who had not previously received D for mCRPC (NCT02494921). Pts were treated with escalating doses of R in combination with D + P for 6-9 cycles, followed by single agent maintenance R until radiographic or clinical PD. The Ph 2 primary endpoint was 6-month (mo) radiographic progression-free survival (rPFS) rate by PCWG2 criteria, with a target rate of 55% and null hypothesis of 35%. Ph 2 pts underwent baseline circulating tumor cell (CTC) enumeration and genome sequencing (Epic Sciences). Cox proportional hazard model and log-rank test were used to test for associations between rPFS and CTC burden and copy number (CN) variants, respectively. Results: 43 pts were enrolled from 11/2015 to 6/2019. Median age was 68 (range 55-84). 20.9% of pts had visceral metastases. 33 (77%) had PD on prior abiraterone, 27 (63%) on enzalutamide, and 17 (40%) on both. In Ph 1b, 19 pts were enrolled. In the first cohort (D 75 mg/m2 day [d] 1, R 200 mg/d d2-14 of every 21d cycle), 2 pts experienced DLTs (febrile neutropenia [FN] and grade 4 neutropenia). With an alternative dosing schema of D 60 mg/m2 on d1, and R daily on d1-4 and 8-15 of cycle, with daily G-CSF support on d5-7, the MTD was not reached and D 60 mg/m2 + R 400 mg/d was chosen as the recommended Ph 2 dose (RP2D). In total, 30 pts were treated at RP2D; median number of D cycles was 8.5 and 60% went on to receive maintenance R. The Ph 2 primary endpoint was met with a 6-mo rPFS rate of 65% (95% CI 50-85%). Median rPFS was 8.0 mos (95% CI 4.1-10.0). PSA response rate (RR) defined as ≥50% reduction was 27.6% (95% CI 12.7-47.2%) and objective RR was 30.8% (95% CI 9.1-61.4%). Among pts treated at RP2D, the most common grade ≥3 treatment-related adverse events were neutropenia (n= 11, 36.7%), lymphocytopenia (n=3, 10%); no cases of FN were observed. Baseline CTC burden was associated with an increased risk of radiographic PD or death (HR 1.038, 95% CI 1.001-1.074, p = 0.038). Pts harboring CTCs without MYC (4/11 pts) or CDK6 CN gain (7/11 pts) had prolonged rPFS compared to those with gene amplification (median rPFS 10.76 vs 4.11 mos, p = 0.03, and 7.01 vs 1.92 mos, p = 0.053, respectively). Conclusions: The combination of R + D was well tolerated and showed promising activity in mCRPC pts who had progressed on an ARSi. The Ph 2 study met its primary endpoint, with an encouraging 6-mo rPFS rate of 65%. Lack of MYC or CDK6 amplification on CTC sequencing was associated with longer rPFS. Funding: Novartis Pharmaceuticals, PCF YIA. Managed by the PCCTC. Clinical trial information: NCT02494921.

Updated results of phase II trial using escalating doses of neoadjuvant atezolizumab for cisplatin-ineligible patients with nonmetastatic urothelial cancer (NCT02451423)

e16510

Background: Patients (pts) with muscle-invasive bladder cancer (MIBC) ineligible for cisplatin-based chemotherapy have no standard systemic therapy options and are prioritized for radical cystectomy (RC) alone. This prospective clinical trial investigated the safety and efficacy of escalating doses of neoadjuvant atezolizumab (N-ATZ) prior to RC in MIBC pts. Methods: This is a single-institution, phase II trial of escalating doses of N-ATZ (1200 mg IV every 3 weeks) in pts with MIBC. Key inclusion criteria were resectable urothelial carcinoma of the bladder (T2-T4a,N0-1,M0) and inability to receive cisplatin-based treatment (eGFR < 60 mL/min, G≥2 neuropathy/hearing loss, pt decision). Pts with high-risk disease at RC were eligible to receive adjuvant ATZ for up to 16 total doses. Pts were followed for up to 2 years following RC. Primary efficacy endpoint was pathologic complete response (pCR; pT0N0). Secondary endpoints were safety of treatment, rate of pathologic downstaging (≤pT1N0), response based on PD-L1 status, and overall survival (OS) and recurrence-free survival (RFS) at 1 and 2 years from RC. Results: A total of 20 pts were enrolled and sequentially treated with one (n=6), two (n=5), and three (n=9) cycles of N-ATZ prior to RC. Median age was 69 (range 61-81), 75% were male and 85% Caucasian. Pts were cisplatin-ineligible due to low GFR (35%), hearing loss (25%) or neuropathy (10%); the rest refused cisplatin (30%). Most pts had pT2 disease (80%); the remainder, pT3/pT4 (15%/5%), and 10% had cN1. Among 17 pts with available tumor PD-L1 status, 76% had PD-L1 positive (CPS≥10) tumors. pCR was observed in 2 pts (10%) with 1 and 2 ATZ doses, whereas pathologic downstaging was observed in 5 pts (25%) across all 3 doses (Table). All pts completed intended treatment and RC within the trial-defined timeframe. Perioperative TRAEs of any grade occurred in 75%, but only 10% had G3 TRAEs (diarrhea, fecal incontinence). There were no G4/G5 events. Median follow-up from RC was 23.6 months and 75% were still followed at the time of data cutoff in 2/2021. Among evaluable pts, 1-year RFS and OS were 72% and 94% while 2-year RFS and OS were 64% and 69%. PD-L1 positive pts had superior OS (logrank p=0.06) and RFS (p=0.10) relative to PD-L1 negative pts. Conclusions: N-ATZ was well tolerated at all three dose levels and did not delay or prevent surgery. As few as 1 to 2 ATZ doses resulted in pathologic downstaging, including pCR. Although pCR rate in this trial was lower than expected, most pts had a durable recurrence-free period and all evaluable pts with tumor downstaging were alive and recurrence-free at 2 years following RC. Increased tumor PD-L1 expression was suggestive of improved outcomes and further biomarker analyses are ongoing. Clinical trial information: NCT02451423. [Table: see text]

Immunogenic priming with 177Lu-PSMA-617 plus pembrolizumab in metastatic castration resistant prostate cancer (mCRPC): A phase 1b study

5053

Background: Immune checkpoint inhibitors have limited single agent activity in microsatellite-stable mCRPC. 177Lu-PSMA-617 (Lu) is a PSMA-targeting radioligand therapy that has demonstrated promising anti-tumor activity. We sought to determine whether a single dose of Lu can induce an immunogenic priming effect to improve outcomes of men with mCRPC subsequently treated with pembrolizumab (P). Methods: We undertook a phase 1b, single arm trial enrolling chemotherapy-naïve mCRPC patients (pts) with progression (PD) on at least one prior androgen signaling inhibitor (NCT03805594). Pts were required to have ≥ 3 PSMA-avid lesions on 68Ga-PSMA-11 PET and measurable disease by RECIST 1.1 criteria. No genomic selection was undertaken. Pts were enrolled sequentially on one of three schedules: A) Single dose of Lu (7.4 GBq) followed by initiation of P (200 mg IV q 3 weeks) 28 days later; B) Lu x 1 dose given concomitantly with first P administration; C) Lu x 1 dose given on C2D1 following initiation of P on C1D1. Pts were treated with P until confirmed radiographic or clinical PD. The primary endpoint was safety; key secondary endpoints included PSA response, objective response rate by RECIST 1.1 criteria (ORR), median duration of response (DOR), and radiographic progression-free survival (rPFS). Results: 18 pts were enrolled, 6 per schedule. The median age was 64 (range 51 – 80) and 44% of pts had visceral metastases. The median baseline number of PSMA-avid metastatic lesions was 20 (range 6 – 50+). Six pts (33%) had progressed on prior abiraterone, 4 (22%) on enzalutamide, and 8 (44%) on both. There were no dose-limiting toxicities and one Grade ≥ 3 treatment-related adverse event (AE) (inflammatory arthritis, schedule B). There were no grade ≥ 3 hematologic AEs. The ORR was 8/18 (44%) and median DOR has not been reached (range 1.9+ – 15.9+ months). Four pts (2 on schedule A, 1 on schedule B, 1 on schedule C) with durable partial responses remain on study treatment for 5.4+, 8.9+, 9.2+, and 17.8+ months, respectively. The median rPFS was 6.5 months (95% CI: 2.5 – 9.8). PSA30, PSA50, and PSA90 response rates were 44%, 28%, and 17%, respectively. Fourteen pts (78%), including all durable responders, had somatic genomic data available. One (7%) harbored a DNA repair mutation ( BRCA1, non-responder), none were MSI-high, and all carried low tumor mutational burden (≤ 5 mutations/MB). Single cell sequencing of the immune microenvironment from paired metastatic tumor biopsies is underway. Conclusions: 177Lu-PSMA-617 as a priming dose followed by pembrolizumab was well tolerated and leads to durable responses in a subset of mCRPC without high mutational burden or microsatellite instability, suggesting a possible immunogenic priming effect of radioligand therapy. Further evaluation of the combination is ongoing in a phase 2 study. Clinical trial information: NCT03805594.

Rate of skeletal-related events (SREs) for abiraterone acetate (AA) versus enzalutamide (ENZ) in prostate cancer: A population-based study using the SEER-Medicare database

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Background: Skeletal-related events are common in men with prostate cancer, and are associated with significant morbidity and mortality. AA and ENZ are novel androgen signaling inhibitors used in the treatment of metastatic prostate castration-resistant prostate cancer (mCRPC). As directly comparative efficacy data do not exist between AA and ENZ, the differing toxicity profiles inform treatment selection. It is unknown whether SRE rates differ in a real-world population between AA, which is given with corticosteroids, and ENZ, which is associated with imbalance and falls. Methods: The national SEER-Medicare linked database was used to identify men with prostate cancer who received AA or ENZ between 2011-2015; approval during this period was solely for mCRPC. Inclusion criteria included Medicare Part A+B coverage 1 year before and after first receipt of AA/ENZ, without any HMO enrollment. Baseline demographic and comorbidity data were gathered. Diagnosis and procedure claims codes were used to identify SREs, defined as pathologic fracture, surgery to bone, radiation to bone, or spinal cord compression. The time to SRE was defined as time from first receipt of AA/ENZ to the first SRE of any type. A multivariable competing risk regression analysis including death as a competing risk was performed. Results: 5,856 men with prostate cancer who first received AA (N = 4,207) or ENZ (N = 1,649) were identified. The median age at initiation of AA/ENZ was 70 years (range 65-101); 78% were White, 12% Black, 4% Hispanic, 3% Asian, and 4% Other. The median follow-up was 14 months. The overall SRE rate was 13.1% after AA/ENZ start: 574 (13.6%) AA and 194 (11.8%) ENZ, with a cumulative incidence of 11.9% at 2 years. Median overall survival was 16 months (14.4 months for AA and 18.3 months for ENZ). Age, stage at diagnosis, race/ethnicity, baseline comorbidities, and prior history of SRE were balanced between AA vs ENZ, aside from baseline osteoarthritis or rheumatoid arthritis (48.0% AA vs 53.2% ENZ, P < 0.001) and baseline Alzheimer’s dementia (9.2% AA vs 11.1% ENZ, P = 0.03). After controlling for these potential risk factors, receipt of AA versus ENZ was not associated with time to SRE (relative risk ratio [RR] = 0.90, 95% CI 0.77-1.06, P = 0.22). Osteoporosis (RR 1.22, 95% CI 1.01-1.49, P = 0.04), osteoarthritis or rheumatoid arthritis (RR 1.23, 95% CI 1.06-1.43, P < 0.01), and prior history of SRE (RR 1.31, 95% CI 1.07-1.59, P < 0.01) were statistically significant risk factors for SRE. Conclusions: In this real-world population of men with prostate cancer, there was no difference in time to SRE between AA and ENZ. Clinical decision-making on whether to prescribe AA or ENZ should be informed by other potential toxicities as well as cross-resistance with sequencing of these therapies. Analysis of impact of bone protective agent use is underway.

The impact of prior radiation therapy on outcome in a phase 2 trial combining sipuleucel-T (SipT) and ipilimumab (Ipi) in patients (pts) with metastatic castration resistant prostate cancer (mCRPC)

5045

Background: SipT is an FDA-approved autologous cellular immunotherapy targeting Prostatic Acid Phosphatase (PAP) that improves survival in patients with mCRPC. Combining immunotherapies could provide opportunities to enhance efficacy. We performed a randomized phase II trial adding CTLA-4 blockade with Ipi following SipT treatment and assessed whether timing of this sequence could modify immune and/or clinical responses to this treatment. Methods: Fifty chemotherapy-naïve mCRPC pts were randomized to receive ipi (4 doses of 3mg/kg every 3 weeks) either immediately (n = 24) or 3 weeks (n = 26) following completion of sipT. Blood was collected at various time points of the study. Immune-related adverse events (irAE) were recorded. The primary endpoint was to determine the proportion of pts who achieved an antibody titer of ³1:400 to PA2024, the targeting cassette in SipT and/or PAP. Clinical response was defined as ³30% reduction in serum prostate specific antigen (PSA) compared to pre-treatment levels. Radiographic progression-free survival (rPFS) and overall survival (OS) were defined as from the date of randomization to the date of radiographic progression and the date of death, respectively, or last follow-up date. Luminex assays for anti-PAP and anti-PA2024 specific serum IgG and ELISpot for IFN-g production against PAP and PA2024 were used to assess antigen-specific B and T cells responses, respectively. Modulation of circulating immune cells was evaluated by CyTOF. Results: SipT + Ipi did not induce any unexpected irAEs. The timing of Ipi did not significantly alter the rates of clinical response, rPFS, OS, toxicity, nor antigen-specific B and T cell responses. Clinical responses were observed in 6 of 50 (12%) pts and were often durable (median 140 days, range 55-689 days). Pts experiencing irAEs were more likely to have a PSA response (P = 0.001). The median rPFS was 5.7 months (mos). The median OS was 31.9 mos. This treatment induced antibody and T cell immune responses irrespective of treatment arm. Single cell assessment bt CyTOF demonstrated that treatment induced CD4 and CD8 T cell activation that was more pronounced with the immediate schedule. Lower frequencies of CTLA-4 positive circulating T cells were associated with better clinical outcomes even at baseline. Lower frequencies of CTLA-4 positive T cells was associated with prior radiation therapy. Prior radiation treatment was associated with improved rPFS (6.5 vs. 3.9 mos, P = 0.004). Conclusions: These findings suggest that pre-existing immunity may help dictate responsiveness to Ipi and SipT combination immunotherapy in mCRPC pts. Prior radiation therapy seems to leave not only a lasting impression on the T cell compartment, but also can associate with improved clinical outcomes with subsequent immunotherapy. Clinical trial information: NCT01804465.

Patterns in cancer management changes for patients with COVID-19 in northern California

1535

Background: The COVID-19 pandemic affected oncology practice in ways that are still evolving. In particular, COVID-19 has led to changes in cancer treatment for patients (pts) infected with COVID, which may have long-term implications for both COVID and cancer-related outcomes. In this retrospective analysis, we describe changes in cancer management over time for cancer pts diagnosed with COVID-19 at two academic institutions in Northern California. Methods: Adult and pediatric pts diagnosed with COVID-19 receiving active cancer management, defined as therapy/surgery/diagnostics within 3 weeks of COVID diagnosis, were identified through the EMR. Patients whose care was affected by COVID-19 were identified and analyzed for significant intra-group differences with regards to management type, treatment intent, and the time of COVID-19 diagnosis (“early” was defined as March to June 2020 and “late” as July 2020 to January 2021). The duration and characteristics of such changes were compared across subgroups. Chi-squared test was used to compare the incidence of delays between subgroups. Results: Among 134 COVID-positive pts on active cancer management, 83 (62%) had significant changes in management that consisted primarily of treatment delays. More delays were identified in patients treated with curative intent earlier in the course of the pandemic compared to later (OR 4.1, p=0.022). This difference was not seen among pts treated with palliative intent. In addition, pts on oral (PO) therapy were significantly less likely to have treatment changes than those on IV/IM therapy (OR 0.32, p=0.005). This difference was driven by a decrease in management changes for those on PO therapy in the later time period (OR 0.27, p=0.026). Pts diagnosed later were more likely to have delays due to clinical reasons rather than institutional policy (OR 6.2, P<.005). The median delay in both time frames was 21 days. Comparison of subgroups is shown in the table. Conclusions: We found significant changes in management of cancer pts with COVID-19 that evolved over time. Oncologists have become increasingly willing to continue therapy for cancer pts treated with curative intent and pts on oral therapy. Changes in cancer therapy have become more frequently related to patient clinical status, and less so due to institutional policies. It will be important to analyze how these changes in management are ultimately reflected in cancer outcomes in order to equip patients and oncologists to react to the next pandemic.[Table: see text]

Phase II trial of escalating doses of neoadjuvant atezolizumab for patients with non-metastatic urothelial carcinoma ineligible for cisplatin-based neoadjuvant chemotherapy

442

Background: For patients (pts) with muscle-invasive bladder cancer (MIBC) who are ineligible for cisplatin-based chemotherapy (cisplatin), the standard of care option is radical cystectomy (RC) alone. This prospective clinical trial investigated the safety and efficacy of escalating doses of atezolizumab (ATZ) as neoadjuvant therapy prior to RC in pts with non-metastatic urothelial cancer. Methods: This single-arm, single institution, phase II trial investigated the administration of one (n = 6), two (n = 5) or three (n = 9) cycles of ATZ (1200 mg IV given every 3 weeks) in pts with MIBC who are either ineligible for or refused cisplatin prior to RC. Key inclusion criteria were urothelial carcinoma of the bladder (T2-T4a,N0-1,M0) and inability to receive cisplatin-based treatment (eGFR < 60 mL/min, G≥2 neuropathy/hearing loss, pt decision). Pts with high-risk disease ( > pT2 or LN+) at the time of RC were eligible to receive adjuvant ATZ for up to 16 total cycles. Primary efficacy endpoint was pathologic complete response (pCR; pT0N0). Important secondary endpoints were safety of treatment, rates of pathologic downstaging and biomarker assessments in serial tissue samples. Pts were followed for up to 2 years following RC. Results: Among 20 pts with MIBC, median age was 69 (range 61-81) and 75% were male. Most commonly pts were cisplatin-ineligible due to low GFR (35%), hearing loss (25%) or neuropathy (10%); remainder refused cisplatin (30%). At trial enrollment, pT2, pT3, and pT4 was present in 80%, 15%, and 5% of pts and 10% had enlarged pelvic lymph nodes ( > 10 mm) on scans. All pts completed intended treatment cycles and all had RC within the defined timeframe ( > 3 weeks from last and < 12 weeks from first treatment). pCR at RC was 10% (2/20 pts), and was observed in pts receiving 1 and 2 cycles of ATZ. Pathologic downstaging (≤pT1N0) was achieved in 25% (5/20 pts) and observed across all three dose levels. Adjuvant ATZ was given to 8 pts. TRAEs of any grade during perioperative period occurred in 75% and G3 TRAEs in 10% (diarrhea, fecal incontinence). There were no G4 or G5 events. Median follow-up from the time of RC was 21.4 months at the time of data cutoff in 10/2020. Among evaluable pts, 1-year RFS and OS were 71% and 94% while 2-year RFS and OS were 64% and 75%. Conclusions: This prospective trial supports the safety and efficacy of ATZ as neoadjuvant therapy in MIBC. Although pCR and rates of downstaging were lower than what was previously reported in comparable neoadjuvant trials of checkpoint inhibitors in MIBC, pCRs in this trial were seen even in pts receiving only 1-2 doses of ATZ. Many pts had a durable recurrence-free period and all 4 evaluable pts who had pathologic downstaging were alive and disease free at 2 years post RC. Translational and biomarker work from this study is also being pursued. Clinical trial information: NCT02451423.

Implementation of clinician-facing prostate cancer therapeutic clinical trial decision tool at a comprehensive cancer center

19

Background: The conventional model for clinical trial (CT) recruitment relies on clinicians to identify potential CTs for patients. Internet technology can be leveraged as a decision tool to enhance the CT recruitment process. Methods: An internet-based, clinician-facing decision tool was developed in genitourinary medical oncology clinic at a Comprehensive Cancer Center (CCC). The tool provided access to a real-time, tailored list of treatment CTs actively recruiting patients with PCa at the CCC based on clinical characteristics inputted by user. The clinical data was summarized. All clinicians (n = 9) with access to the decision tool completed a survey to assess effectiveness and satisfaction. Results: During a 9-month pilot period, user engagement increased from a baseline of 36 to 136 cases per month, with a total of 644 cases overall. Among cases, 525 had metastatic disease, 436 of which were metastatic castration resistant PCa (mCRPC). Overall, 145 cases were classified as having oligo-metastatic ( < = 3) PCa, 93 of whom were also mCRPC. Prior treatments received included abiraterone in hormone-sensitive PCa (HSPC 19.3%, CRPC 48.7%); enzalutamide (HSPC 3.7%, CRPC 34.9%) apalutamide (HSPC 1.3%, CRPC 6.9%), taxane (HSPC 17.2%, CRPC 27.8%), radium-223 (6.1%), sipuleucel-T (18.3%), parp inhibitors (4%), or check-point inhibitors (6%). Clinician-inputted genomics of cases included CDK12 (20.9%), MSI-high disease (13.6%), BRCA1/2 (32.7%), ARID1a (7.3%), ATM (21.8%), FANCA (4.5%), or CHEK2 (6.4%) and HDAC2 (0.9%). Among survey respondents, use of tool in clinic was reported sometimes (22%), often/always (78%). Results of decision tool were reported to inform treatment sometimes (22%) or often/always (78%). Respondents confidence in often/always knowing all available CTs increased from a baseline of 0% to 89%, and 89% of users reported very/complete satisfaction with decision tool. Conclusions: An internet-based CT decision tool for provides detailed clinical characteristics of patients for whom CTs are being considered at a CCC. Clinicians using the decision tool report high levels of satisfaction. The tool was effective in increasing confidence in knowledge of current available CTs. Data gathered in the decision tool may inform future CT development. Future research with expanded use of decision tool among referring clinicians will assess its impact in promoting diversity among CT participants.

Molecular determinants associated with long-term response to apalutamide (APA) in nonmetastatic castration-resistant prostate cancer (nmCRPC)

8

Background: SPARTAN, a phase 3 placebo (PBO)-controlled study in patients (pts) with nmCRPC, showed that APA plus androgen deprivation therapy (ADT) significantly improves metastasis-free survival compared with PBO + ADT. This exploratory analysis investigated potential biological signatures of pts with long-term responses to APA and PBO. Methods: The biomarker cohort of SPARTAN was characterized as long-term responders (LTR) or early progressors (EP) based on time to metastasis, and separated into quartiles for APA and PBO groups. Pts progressing in the first quartile (APA, 21; PBO, 17), with shortest time to metastatic event, were classified as EP, those progressing in the last quartile (APA, 39; PBO, 20) as LTR. Gene expression profiles were generated from 233 archival primary prostate tumors. Predefined gene signatures indicative of cancer biology were compared between LTR and EP groups within the APA and PBO arms using 2 sample t tests. Signatures associated with LTR and EP were identified using p values of less than 0.05. Results: Median time to metastatic progression was 40.5 months in APA pts and 22 months in PBO pts in the LTR group and 7.3 and 3.6 months in APA and PBO pts, respectively, in the EP group. Signatures categorized into 3 general mechanistic classes (immune regulation, proliferation, and hormone dependence) associated with LTR on APA included increased T cell activity reflected by T cell activation ( p = 0.0045), stimulation ( p = 0.0642), cytokine response ( p = 0.0489), and interferon production (gamma response p = 0.0227 ), and decreased T cell exclusion ( p = 0.0652), low proliferative capacity ( p = 0.0435), and increased hormonal dependence ( p = 0.0485). High risk (DECIPHER p = 0.0406, metastatic potential p = 0.0077), hormone nonresponsive (basal p = 0.0115; androgen receptor activity-low, p = 0.0437), and neuroendocrine-like tumors ( p = 0.0125) were associated with early progression on treatment with PBO. Conclusions: Although the data require confirmation in larger studies, these molecular determinants may have utility in selecting pts with nmCRPC who may derive the most benefit from APA and other androgen signaling inhibitors. Clinical trial information: NCT01946204.

5-hydroxymethylcytosine as a liquid biopsy biomarker in mCRPC

148

Background: 5-hydroxymethylcytosine (5hmC) is an epigenetic modification which regulates gene expression and is associated with active transcription. The optimization of 5hmC sequencing in cell-free DNA (cfDNA) could therefore enable assessment of gene activity through a liquid biopsy. We aimed to investigate the 5hmC landscape of metastatic castration-resistant prostate cancer (mCRPC) and to evaluate the potential of 5hmC modifications in cfDNA as biomarkers of outcome in mCRPC patients. Methods: Genome-wide 5hmC modifications were analyzed with a low-input whole-genome 5hmC sequencing method based on selective chemical labeling in DNA from 93 mCRPC tissue biopsies previously profiled with whole-genome sequencing (WGS), RNA-sequencing and whole-genome bisulfite sequencing (WGBS). In addition, we analyzed 64 cell-free DNA (cfDNA) samples, from men with mCRPC before first-line abiraterone or enzalutamide, with both 5hmC sequencing and a conventional targeted ctDNA panel assessing common genomic alterations. Results: In mCRPC tissue samples, 5hmC enrichment was more strongly associated with gene expression than promoter methylation or copy number. Among cancer hallmark pathways, the androgen response genes had the strongest association between 5hmC and gene expression, suggesting a disease specific marking of gene activation. 5hmC patterns in cfDNA could be used to estimate the circulating tumor DNA fraction (ct-fraction), which was prognostic for overall survival (tertiles of ct-fraction, HR = 1.6 95%CI 1.1-2.3, p = 0.007). Further, 5hmC levels were indicative of gain of oncogene activity (such as AR, MYC, and PIK3CA) and loss of tumor suppressor gene activity (such as RB1, TP53 and BRCA2). The number of alterations, by 5hmC levels, of common drivers of mCRPC was prognostic for overall survival, also after adjusting for ct-fraction (adjusted p = 0.00001), and the prognostic value of common alterations detected by 5hmC sequencing versus conventional targeted ctDNA sequencing was similar. Finally, 5hmC levels in cfDNA of genes not significantly altered by copy number gain or loss (and thus not routinely included in targeted ctDNA sequencing assays), such as TOP2A and EZH2, identified a high-risk subgroup of mCRPC, which was highly prognostic for overall survival independent of ct-fraction (adjusted HR = 1.8 95%CI 1.2-2.8, p = 0.007). Conclusions: 5hmC in mCRPC tissue demonstrated an association with gene expression that was highest for prostate cancer driver genes, highlighting the ability to track disease-specific biology. 5hmC in cfDNA from men with mCRPC can be used to estimate the ct-fraction of the sample, infer activity gain and loss of common drivers of mCRPC, and identify high-risk groups of mCRPC based on alterations not commonly detected with conventional ctDNA sequencing, showing its potential as a liquid biomarker. Further studies are aimed at optimizing and validating 5hmC-based biomarkers in larger cohorts.

Feasibility study of gallium-68 citrate PET as a bone-tropic imaging biomarker in mCRPC

31

Background: Transferrin receptor (TFRC) expression is controlled by the PI3K and MYC signaling pathways, which are frequently dysregulated in prostate cancer (PC). Gallium-68 citrate (68Ga-citrate) is an iron biomimetic, which can be used to image PC in a TFRC dependent fashion. We performed a single-center pilot imaging study to investigate the use of 68Ga-citrate PET in patients with metastatic castration-resistant PC (mCRPC). Methods: Following written informed consent, mCRPC patients were prospectively enrolled and underwent 68Ga-citrate PET imaging. Optional metastatic tumor biopsies were undertaken at the time of imaging. Results: 34 mCRPC patients underwent 68Ga-citrate PET imaging. The median age was 67.5 years old. Median duration of castration resistance was 17.5 months; 14.7% of patients were post-docetaxel. Median serum PSA was 35.2 ng/dL. A total of 483 lesions were detected on conventional imaging (CT, 99mTc-HDP) or 68Ga-citrate PET, including 420 osseous and 63 soft tissue (nodal and visceral) lesions (Table). 67.3% of all lesions were detected on 68Ga-citrate PET, including 74.5% of all osseous lesions but only 19.0% of all soft tissue lesions (p<0.0001). Eight (1.7%) lesions were detected on 68Ga-citrate PET imaging only. Per-lesion average SUVmax (SUVmax,avg) was 6.7. Metastatic biopsies of PET avid lesions were performed in 20 patients (59%); adenocarcinoma histology was confirmed in 14 (70%) cases, treatment-emergent small cell neuroendocrine cancer (t-SCNC) in 6 (30%). There was no significant difference in SUVmax,avg between patients with adenocarcinoma or t-SCNC (SUVmax,avg 7.3 vs 7.6, respectively; Table). Serial 68Ga-citrate PET perfomed in a patient with biopsy-confirmed t-SCNC after 2 cycles of carboplatin/cabazitaxel demonstrated an early metabolic response (28.5% decrease in average SUVmax) confirmed on subsequent conventional imaging. Conclusions: 68Ga-citrate PET detects mCRPC bone metastases in patients with biopsy-proven prostatic adenocarcinoma or t-SCNC, distinguishing it from lineage dependent agents such as PSMA tracers. Detection of an early metabolic response in the bone of a treated t-SCNC patient was observed. Further prospective studies are ongoing coupling serial Ga-citrate PET with investigational agents targeting the MYC signaling pathway. Clinical trial information: NCT02391025. [Table: see text]

Assessing the impact of the COVID-19 pandemic on patients with genitourinary malignancies

38

Background: The COVID-19 pandemic has vast implications on the health system. Patients with a cancer diagnosis may face greater challenges in the context of the current COVID-19 pandemic. Methods: We sought to assess the impact of the COVID-19 pandemic among patients with genitourinary malignancies. We performed a cross-sectional survey study at a Comprehensive Cancer Center during the current pandemic. Results: A total of 86 participants were recruited to the study to date, 72.1% had prostate, 19.8% had kidney, and 12.8% had bladder cancer. A subset (n = 5) had more than one primary tumor. The mean time from diagnosis was 6.47 years (std dev 6.01, range from 0 to 27 years). Overall, 73% reported having metastatic disease and prior treatment with surgery (62%), radiation (71%), or systemic therapy (68%), with 68.6% currently receiving cancer treatment. In the study, 78.9% of patients were >65 years of age and 88.2% were White. The majority of participants had a bachelor’s degree or higher level of education (74.4%), were legally married (82.6%), were homeowners (91.9%), and reported an annual household income of >$100,000 (56.0%). Among respondents, 7% reported loss/change of health insurance and 30% reported a decrease in household income. Among patients with reduced household income, 23% reported a reduction of more than 50%. In this study, 28% of patients reported that the pandemic impacted their cancer treatment. Overall 7% reported decrease in frequency of labs, 11% reported a delay in obtaining a scan, 5% reported treatment delays, and 96% reported use of telemedicine (video or telephone) visit. Overall, 59% reported fear of hospitalization, 23% reported delays in seeking medical care, and 16% reported missing required medications. Conclusions: The negative impact of the COVID-19 pandemic on patients with genitourinary malignancies is extensive. Ongoing research is evaluating the impact across socio-demographically groups and examine clinical outcomes associated with delays in care and medication non-adherence.

Androgen deprivation therapy and risk of SARS-CoV-2 infection in men with prostate cancer: A University of California (UC) Health System registry study

37

Background: SARS-CoV-2 entry into host cells is facilitated by the transmembrane protease TMPRSS2. TMPRSS2 expression can be modulated by the androgen receptor. It is unclear whether androgen deprivation therapy (ADT) may partially protect from SARS-CoV-2 infection. Methods: A retrospective registry study of adult men with prostate cancer who underwent testing for SARS-CoV-2 in the UC Health System between February 1, 2020 and October 6, 2020 was performed. The University of California Health COVID Research Data Set (UC CORDS), which includes electronic health data of all patients who underwent testing for SARS-CoV-2 at 5 UC academic medical centers (UC Davis, UC Irvine, UC Los Angeles, UC San Diego, and UC San Francisco) and 12 affiliated hospitals across California, was used. Association of SARS-CoV-2 infection and receipt of ADT (GnRH agonist or antagonist) within 90 days of COVID testing was determined using the Chi-Squared test. Analyses (Chi-Squared or Fisher’s exact tests) were also performed in race/ethnicity subgroups. Results: Overall, 2,948 men with prostate cancer who underwent SARS-CoV-2 testing were identified, of whom 59 (2.0%) tested positive. Of the 2,948 men, 2,124 (72%) were White; 219 (7%) Black or African-American; 182 (6%) Asian or Native Hawaiian/Pacific-Islander; 176 (6%) Other race; and 247 (8%) Unknown race. There were 235 (8%) Hispanic or Latino men. Among the 444 men who received ADT in the entire cohort, 7 (1.6%) tested positive, and among the 2,504 men who did not receive ADT, 52 (2.1%) tested positive (OR 0.76, 95% CI 0.34-1.67, P = 0.49). No statistically significant association between ADT and SARS-CoV-2 positivity was found within race or ethnicity subgroups. Conclusions: No association between the use of ADT and the risk of testing positive for SARS-CoV-2 was identified in this study of a diverse patient population in the University of California Health System medical centers and hospitals. In this setting of an overall low prevalence of SARS-CoV-2 infection, thus far, there is no strong evidence of a protective benefit of ADT.

TERT promoter mutation as a prognostic marker in patients with advanced urothelial carcinoma treated with immune checkpoint inhibitors

476

Background: Reliable predictive markers are lacking in patients (pts) with locally advanced or metastatic urothelial carcinoma (aUC) treated with immune checkpoint inhibitors (ICI). We sought to determine whether specific genomic alterations could be used to predict overall survival (OS) in this patient population. Methods: We undertook a retrospective cohort study of pts with aUC who received ICI and underwent genomic profiling by next-generation sequencing (NGS). All patients underwent NGS using commercially available platforms (e.g. Foundation Medicine, Strata, Invitae), or testing on the CLIA-certified institutional panel UCSF500. Associations between the 20 most frequently altered genes and OS were first examined by Cox regression. Genes with a p <0.1 on univariate analysis and relevant clinical variables were then included in a multivariable analysis. Results: We identified 78 pts treated with ICI for aUC with available genomic profiling results. Median age at ICI initiation was 71; the majority of patients had visceral metastases (70.5%), ECOG performance status ≤1 (62.8%) and received ICI in the post-platinum setting (52.6%). Objective response rate in this cohort was 35.9%, median progression free survival was 4.0 months (95% CI 2.6-10.5) and median OS was 17.5 months (95% CI 14.1-NR) from ICI start. The most commonly altered genes were the TERT promoter (TERTp) (61%), TP53 (52%), RB1 (31%), CDKN2A(29%) and CDKN2B (27%). On univariable analysis there was a trend towards longer OS in pts with TERTp mutations (HR 0.53, 95% CI 0.27-1.06, p = 0.07), and shorter OS in pts with CDKN2B mutations (HR 1.91, 95% CI 0.98-3.73, p = 0.06). Both mutations were included in a multivariable analysis. After adjusting for known prognostic variables (ECOG PS, visceral metastases, albumin, hemoglobin, body mass index [BMI], neutrophil to lymphocyte ratio [NLR], and histology), the presence of a TERTp mutation was significantly associated with improved OS (HR 0.30, 95% CI 0.10-0.93, p = 0.04; Table). Conclusions: The presence of a TERTp mutation was an independent predictor of improved OS in a cohort of aUC pts treated with ICI. Other common mutations and clinical variables were not associated with OS on a multivariable analysis. These findings are hypothesis-generating and prospective validation is needed. [Table: see text]

Streamlining the genetics pipeline to increase testing for patients at risk for hereditary prostate cancer

66

Background: At UCSF, ~850 men with metastatic prostate cancer are seen annually, all of whom should receive germline genetic testing. Prior to our study, the GU medical oncology program offered a self-pay, take-home genetic testing kit (30-gene panel) to patients with metastatic prostate cancer. Patients with positive test results were referred for genetic counseling. For this study, the UCSF Cancer Genetics and Prevention program partnered with the GU medical oncology program, adapting a Genetic Testing Station (GTS) to expand access and accommodate testing needs. At Prostate GTS, a genetic counselor assistant (GCA) facilitates cancer genetics education by video, enrolls patient in a research registry, collects a family history and saliva sample sent for an 87-gene panel. Our study evaluates the effectiveness of the GTS by comparing prospective performance metrics and testing outcomes of Prostate GTS with retrospective data obtained from the take-home method (“Before GTS”). Methods: Men were ascertained by their treating oncologist and referred for GTS. Indications for genetic testing include: all metastatic prostate cancer, or under age 50 at diagnosis, or with family history, or at clinician discretion. GTS metrics were prospectively collected by clinical staff. “Before GTS” metrics were retrospectively collected through data reporting from commercial lab analysis (test orders dated 01/2017 to 09/2019) and patient chart review. Results: In the first 6 months of Prostate GTS (10/2019-3/2020), 139 patients received testing at the GTS and 91% (127) had received results at censoring. GTS results were distributed as follows: 10% (13) positives, 33% (42) negative no VUS, and 57% (72) negative w/VUS. In the 33 months, “Before GTS”, 218 genetic testing orders had been placed, with 78% (196) reported at censoring, distributed as 11% (22) positive, 68% (134) negative no VUS, and 20% (40) negative w/VUS. The rate of incomplete tests decreased significantly with the GTS, (22% down to 9%, p = 0.0008). "Before GTS", of patients with a positive result, 15/22 (68%) were referred for genetic counseling, of which 8 completed a visit (36% of all positives). In the GTS model, all patients with positive results were seen by a genetic counselor for results disclosure and counseling. Comparing result rates across similar timeframes, 127 results were reported from GTS compared to 40 results from “Before GTS” in the same calendar months the year prior, representing a 218% increase in returned results. Median turnaround time decreased from 16 days to 9 days with GTS. Conclusions: GTS efficiently increased access to genetic testing and counseling for patients with prostate cancer. By leveraging GCAs and video education, this model involves cancer genetics at each step of the process, decreases turnaround time, and increases rates of returned results that can be used by patients to inform treatment and prevention strategies.

Streamlining the genetics pipeline to increase testing for patients at risk for hereditary prostate cancer

1590

Background: Metastatic prostate Cancer (mPCa) is increasingly recognized as a heritable disease and germline genetic testing has increasingly become a part of standard of care. At the University of California at San Francisco (UCSF) Genitourinary (GU) Medical Oncology clinic, approximately 850 new patients with mPCa are seen annually. A feasibility pilot Genetic Testing Station (GTS) was developed to expand access to genetic testing among this high-risk population. GTS is facilitated by Genetic Counselor Assistants (GCA) under the supervision of genetic counselors. Methods: This is a feasibility pilot of a GTS model among patients with mPCa. In this model, all patients with mPCa are offered a same day GTS visit with a GCA. At the GTS, the patient receives pre-test education via videos developed by genetic counselors. The patient provides informed consent, a family history, and a saliva sample for Invitae’s 87-gene panel. All positive results trigger a genetic counselor visit while non-positive results either receive a letter or a genetic counselor visit (in person or via telehealth). To evaluate the model, testing frequency and laboratory turnaround time (TAT) was assessed before and after the pilot. Results: In the first four months of the GTS pilot (10/14/2019 – 02/10/2020), 94 patients were referred and received genetic testing. Eight germline positives were identified (BRCA2, CHEK2, HOXB13 MSH6, RECQL4). The average TAT was 8 days. 9.3% of patients were found to have pathogenic mutations through the prostate GTS which is comparable to previously published rates of germline mutations in metastatic prostate cancer patients. In a 4-month time frame the prior to the intervention (10/01/2018-1/31/2019), 26 genetic testing orders were placed. The average laboratory TAT in this prior process was 17 days. Rates of positive germline mutations in the prior model was 8.6%. Conclusions: The GTS is a feasible method to increase access to germline genetic testing among a high-risk population. It may reduce barriers to testing and facilitate real-time discussion of treatment and prevention strategies with patients and family members. As a result, we will continue to operate the GTS. This model provides a framework for scaling access for and cascade testing in other high-risk patient groups.

Phase 1b study of BXCL701, a novel small molecule inhibitor of dipeptidyl peptidases (DPP), combined with pembrolizumab (pembro), in men with metastatic castration-resistant prostate cancer (mCRPC)

e17581

Background: BXCL701 (talabostat previously PT100) is an oral small molecule inhibitor of DPP4, DPP8 and DPP9, which trigger macrophage cell death via pyroptosis resulting in proinflammatory stimulation of the innate immunity pathway. Expression of PD-L1 correlates with amplification of DPP8 and DPP9. In syngeneic animal models, significant tumor responses were observed when BXCL701 was used with checkpoint inhibition. In a prior clinical study, BXCL701 at a total daily dose of 0.6mg (as 0.3mg BID) demonstrated single agent activity in 2 pts with Stage IV melanoma (unpublished). Methods: In this multi-center study, eligible patients (pts) had progressing mCRPC (PCWG3), at least 1 line of systemic therapy and ≤ 2 lines of cytotoxic chemotherapy for mCRPC, no prior anti-PD-1/PD-L1 or other T-cell directed anti-cancer therapy, and an ECOG PS of ≤ 2. Pts received fixed dose pembro (200mg IV q21 days) with escalating doses of BXCL701 (0.4mg and 0.6mg PO QD days 1-14 of 21-day cycles) using a 3X3 design. The key endpoints were safety and identification of the recommended phase 2 dose (RP2D) for the combination. Composite response (RECIST, PSA, CTC), plasma drug concentration and change in relevant immune effector cytokines were also evaluated. Results: Six pts were treated at 2 BXCL701 dose levels of 0.4mg qd (n = 3) and 0.6mg qd (n = 3), with 5 pts having adeno, 1 pt having mixed adeno and SC-NEPC. Prior tx included ADT (n = 6), 2nd generation androgen signaling inhibitors (n = 4), chemo (n = 4), RT (n = 5). Among 3 pts at the BXCL701 dose level of 0.6mg, 1 pt had a DLT of Grade 3 syncope (C1D6) and 1 pt had fatal acidosis (C3D8). A dose-dependent increase in pts with low-grade on-target clinical effects was observed. In the 0.4mg qd cohort 1 pt had lower extremity (LE) edema. Whereas in the 0.6mg qd cohort, all pts had events consistent with cytokine release: 3 had hypotension and 2 pts each had dizziness and LE edema. The 0.6mg/day dose level was expanded using a split dose strategy to improve tolerability while maintaining the daily dose previously associated with objective responses. BXCL701 was quantifiable in plasma. Conclusions: BXCL701 0.4 mg QD on days 1 to 14 of 21-day cycle plus pembrolizumab 200 mg IV on day 1 every 21 days was well tolerated in pts with mCRPC. A dose-dependent increase in on-target clinical effects expected with cytokine upregulation was seen. The final dose expansion using the split dose for the RP2D, plasma drug concentrations and relevant biomarkers will be presented. Clinical trial information: NCT03910660 .

Prostate-specific antigen (PSA) kinetics in patients (pts) with advanced prostate cancer treated with apalutamide: Results from the TITAN and SPARTAN studies

5541

Background: The phase III TITAN and SPARTAN studies demonstrated improved outcomes with the addition of apalutamide (APA) to androgen deprivation therapy (ADT); outcomes included prolonging overall survival and radiographic progression-free survival (rPFS) in metastatic castration-sensitive prostate cancer (mCSPC) in TITAN, and metastasis-free survival (MFS) in nonmetastatic castration-resistant PC (nmCRPC) in SPARTAN. A post hoc analysis of PSA kinetics in pts from both studies is reported. Methods: Baseline PSA at randomization, time to PSA nadir, and proportion of pts achieving a PSA decline of ≥ 90% (PSA90) and of pts achieving a PSA ≤ 0.2 ng/mL at 3 and 12 months and at any time after treatment in the APA arms of the TITAN and SPARTAN studies were evaluated. Within each study, rPFS/MFS were compared between pts achieving a PSA90 or PSA ≤ 0.2 ng/mL response vs not. Results: 525 TITAN pts and 806 SPARTAN pts treated with APA were included in the analysis. Median baseline PSA, time to PSA nadir, median PSA nadir, and maximum percentage changes from baseline PSA are shown in the table. PSA90 and confirmed PSA ≤ 0.2 ng/mL were evident as early as 3 months in both TITAN and SPARTAN, and percentage of confirmed response continued to increase at 12 months. Pts treated with APA who achieved PSA90 were at lower risk of rPFS events in TITAN and of MFS events in SPARTAN, with a hazard ratio (95% confidence interval) of 0.46 (0.321-0.653) and 0.36 (0.271-0.489) in each respective study (both p < 0.0001), compared with APA pts who did not achieve PSA90. Pts with confirmed PSA ≤ 0.2 ng/mL had similar rPFS and MFS benefits. Conclusions: Pts with advanced PC, whether mCSPC or nmCRPC, treated with APA + ADT demonstrated rapid PSA declines that continued over time. There was a high rate of pts with PSA90 and with PSA ≤ 0.2 ng/mL responses, with a majority of pts reaching PSA90 by 12 months. Pts achieving PSA90 and/or PSA nadir of ≤ 0.2 ng/mL had a prolonged rPFS and MFS in TITAN and SPARTAN, respectively. Clinical trial information: NCT02489318; NCT01946204 . [Table: see text]

Molecular determinants of prostate specific antigen (PSA) kinetics and clinical response to apalutamide (APA) in patients (pts) with nonmetastatic castration-resistant prostate cancer (nmCRPC) in SPARTAN

5521

Background: In SPARTAN, APA + androgen deprivation therapy (ADT) prolonged metastasis-free survival (MFS) and improved PSA kinetics over placebo (PBO) + ADT in high-risk nmCRPC. All molecular subtypes derived benefit in MFS from APA (Feng FY, et al. ASCO GU 2019; abstract 42). We evaluated the association of PSA decline and efficacy outcomes in SPARTAN pts with different molecular subtypes. Methods: Gene expression from archival primary tumors (biomarker population) was assessed with the DECIPHER platform (Decipher Biosciences, Inc.) and stratified into genomic classifier (GC) high- and low-to-average risk using GC score > 0.6 and ≤ 0.6, respectively, and ADT-resistant or -sensitive basal or luminal A/B (PAM50 classifier) subtypes. PSA nadir and confirmed PSA decline (Table) were assessed in APA pts overall and at 3, 6, and 12 mo. Associations between molecular subtypes and outcomes were assessed. Results: Of 233 available samples, 154 were from APA pts; 49% of APA pts had high GC score and 66% had basal subtype. PSA levels at baseline were similar across all subtypes. Regardless of GC score or basal/luminal subtype, > 50% of patients achieved ≥ 90% reduction in PSA with APA. PSA declined faster and PSA reduction was deeper at 6 mo (Table) in GC low to average vs GC high risk and luminal vs basal subtypes. Overall, only luminal vs basal subtypes had a significantly higher % of pts with ≥ 90% PSA decline (Chi square p = 0.037). In luminal pts, deeper PSA decline with APA was consistent with improved MFS vs basal pts. In GC high pts, MFS benefit with APA was similar to that in GC low to average pts despite lower PSA decline. Although GC low to average and luminal pts had more rapid and deeper PSA responses than GC high or basal pts, respectively, all pts derived MFS benefit. Association of long-term outcomes with PSA decline in these molecular subtypes will be presented. Conclusions: In SPARTAN, all molecular subtypes of pts with nmCRPC treated with APA + ADT had MFS benefit and rapid and sustained PSA decline. PSA responses were deepest and most rapid in GC low to average and luminal subtypes. Clinical trial information: NCT01946204 . [Table: see text]

The comprehensive methylation landscape of metastatic castration-resistant prostate cancer (mCRPC) identifies new phenotypic subtypes: Results from the West Coast Prostate Cancer Dream Team (WCDT)

5507

Background: While recent studies have delineated the genomic landscape of mCRPC, its epigenomic landscape has not been as well characterized. The goal of this study was to define the comprehensive methylation landscape of mCRPC. Methods: mCRPC patients (pts) underwent a metastasis biopsy as part of a multi-institutional study (NCT02432001). Deep whole-genome bisulfite sequencing (mean depth 46x) was performed on fresh frozen tissue from 100 mCRPC patients; data was paired with deep whole-genome and transcriptome sequencing from the same samples. Unbiased hierarchical clustering of the mCRPC methylome was undertaken, and the survival of patients in each cluster was calculated using the Kaplan Meier method. Results: Unbiased hierarchical clustering revealed several distinct subtypes. 22% of mCRPC samples exhibited a novel epigenomic subtype associated with hyper-methylation. This hypermethylated (HM) cluster was significantly associated with somatic mutations in genes known to be involved in methylation, eg TET2 and DNMT3B, as well as in genes in which mutations have been associated with hyper-methylation in other cancer types ( IDH1 in glioblastoma and BRAF in colon cancer). mCRPC survival was 56.1 mos in pts with HM cancers compared to 35.6 mos in non-HM (p = .055). Methylome clustering also identified a unique cluster comprised of all patients with treatment-induced small cell/neuroendocrine cancer, a subtype previously associated with poor survival. Conclusions: This integrated study of whole-genome, whole methylome and whole-transcriptome sequencing provides the first comprehensive overview of the important regulatory role of methylation in metastatic castration-resistant prostate cancer, and has identified at least two distinct subtypes. The clinical and therapeutic implications of methylation subtypes should be explored in future studies. Clinical trial information: NCT02432001 .

Correlation of tumor mutational burden (TMB) with molecular profiling and clinical characteristics in patients with bladder cancer

e17025

Background: Bladder cancers (BC) are frequently highly mutated. Next generation sequencing (NGS) can both shed light on mutational burden and the specific alterations that provide insights into the underlying biology of individual tumors. Methods: We retrospectively reviewed BC cases assessed with UCSF500, an institutional NGS assay that uses hybrid capture enrichment of target DNA to interrogate approximately 500 frequently mutated cancer genes. Hypermutated tumors were defined as having TMB > 10 mutations/Mb. Fisher’s exact test was used to compare patients (pts) with hypermutated (HM) and non-hypermutated (NHM) tumors. Results: From 2015 to 2019, 74 pts with BC underwent UCSF500 testing; 48 pts were evaluable for TMB, of which 19 pts (40%) had HM tumors. 17/19 pts were evaluable for mutational signatures; all 17 had APOBEC signatures. Signatures were not assessed in NHM tumors due to low TMB. Clinicopathologic characteristics and most common alterations in the two groups are listed in the table. More HM pts had responses to immunotherapy (IO) treatment (86% vs 40%, p = 0.13). Conclusions: In this single-institution BC cohort, HM tumors were common and APOBEC mutational signature was the common underlying biology in HM tumors. There were relevant differences in common alterations between HM and NHM tumors, including more FGFR3 mutations in NHM tumors. HM status and APOBEC signature were suggested as relevant predictive biomarkers of response to IO, which should be investigated further in larger BC cohorts. [Table: see text]

A phase III randomized, placebo-controlled, double-blind study of niraparib plus abiraterone acetate and prednisone versus abiraterone acetate and prednisone in patients with metastatic prostate cancer (MAGNITUDE)

TPS5588

Background: Preclinical data suggest synergistic antitumor activity when the PARP inhibitor (PARPi) niraparib is combined with the androgen pathway inhibitor abiraterone acetate1. The addition of a PARPi to abiraterone acetate plus prednisone (AAP) showed improved radiographic progression-free survival (rPFS) vs AAP alone in patients with mCRPC regardless of DNA repair gene defect (DRD) status2. Interim results from a phase I study support safety and tolerability of niraparib 200 mg combined with AAP in patients with mCRPC3. The objective of this Phase III study is to compare the efficacy and safety of niraparib plus AAP versus AAP with placebo as first-line therapy for mCRPC. Methods: This ongoing multicenter MAGNITUDE study (NCT03748641) will open in approximately 300 sites across 28 countries and will enroll patients with mCRPC who have not received treatment in the metastatic castrate resistant setting other than ongoing androgen deprivation therapy [ADT] and ≤4 months of AAP. DRD status will be determined by plasma and tissue assays. The cohort with DRD (n=400) and the cohort without DRD (n=600) will each be randomized 1:1 to niraparib + AAP or placebo + AAP. The first patient was consented in February 2019 and enrollment is ongoing. The primary objective of the study is to compare radiographic progression-free survival (rPFS) as assessed by blinded independent central radiology review in each cohort and treatment group. To test superiority of the combination vs AAP, sample sizes were estimated to provide 92% power to detect HR≤0.65 rPFS in the cohort with DRD and 94% power to detect HR≤0.67 in rPFS in the cohort without DRD, both at a 2-tailed level of significance of 0.05. The secondary objectives are time to symptomatic progression, time to cytotoxic chemotherapy, and overall survival. Safety and pharmacokinetic profiles will be evaluated. 1Rajendra N, et al. Cancer Res 2019;79(13 Suppl):Abstract nr 2134. 2Clarke N, et al. Lancet Oncol. 2018;(7):975-986. 3Saad, et al. Ann Oncol, 2018;29 (suppl 8), mdy284.043, https://doi.org/10.1093/annonc/mdy284.043 ) Clinical trial information: NCT03748641 .

Final survival results from SPARTAN, a phase III study of apalutamide (APA) versus placebo (PBO) in patients (pts) with nonmetastatic castration-resistant prostate cancer (nmCRPC)

5516

Background: SPARTAN evaluated APA vs PBO in pts with nmCRPC and a prostate-specific antigen doubling time of ≤ 10 mo receiving androgen deprivation therapy (ADT). At primary end point analysis of metastasis-free survival (MFS), APA significantly improved median MFS by 2 yrs, as well as time to metastasis, progression-free survival, and time to symptomatic progression vs PBO (Smith, et al. NEJM 2018); overall survival (OS) results were immature. SPARTAN was unblinded upon meeting the primary end point; pts still on PBO were allowed to cross over to APA. Final survival results are reported herein. Methods: 1207 nmCRPC pts were randomized 2:1 to APA (240 mg QD) or PBO plus ongoing ADT. At progression, pts could receive open-label sponsor-provided abiraterone acetate + prednisone. After the primary efficacy end point (MFS) was met, 76 PBO pts (19%) crossed over to APA. OS and time to cytotoxic chemotherapy (TTCx) were tested by group sequential testing procedure with O’Brien-Fleming (OBF)-type alpha spending function. Time-to-event end points were analyzed by Kaplan-Meier method and Cox model. A sensitivity analysis for OS, accounting for crossover using a naïve censoring approach, was conducted. Results: With follow-up of 52.0 mo, 428 (of 427 required) OS events had occurred. Median treatment duration: APA, 32.9 mo; PBO, 11.5 mo. Median OS was significantly longer with APA + ADT vs PBO + ADT (73.9 vs 59.9 mo), (hazard ratio [HR], 0.784, Table). APA significantly lengthened TTCx (HR, 0.629). Discontinuation rates (APA vs PBO) due to progressive disease were 42.7% vs 73.9%, and due to adverse events (AE) 15.2% vs 8.4%. Safety was consistent with previous reports; grade 3/4 treatment-emergent (TE) AEs of special interest were rash 5.2%, fractures 4.9%, falls 2.7%, ischemic heart disease 2.6%, hypothyroidism 0%, and seizures 0%. 1 TEAE leading to death (myocardial infarction) was considered potentially APA related. Conclusions: In pts with nmCRPC, APA + ADT significantly improved OS compared with PBO + ADT, with median OS > 6 yr in the APA + ADT group and 14 mo improvement over PBO + ADT. Benefit from APA was observed despite a 19% crossover from PBO. The safety profile of APA was consistent with prior interim analyses. Clinical trial information: NCT01946204 . [Table: see text]

Clinical outcomes in men of diverse ethnic backgrounds with metastatic castration-resistant prostate cancer

BACKGROUND

We have shown previously in multivariable analysis that black men had 19% lower risk of death than white men with metastatic castration-resistant prostate cancer (mCRPC) treated with a docetaxel and prednisone (DP)-based regimen. The primary goal of this analysis was to compare progression-free survival (PFS), biochemical PFS, ≥50% decline in prostate-specific antigen (PSA) from baseline and objective response rate (ORR) in white, black and Asian men with mCRPC treated with a DP-based regimen.

PATIENTS AND METHODS

Individual patient data from 8820 mCRPC men randomized on nine phase III trials to a DP-containing regimen were combined. Race used in the analysis was based on self-report. End points were PFS, biochemical PSA, ≥50% decline in PSA from baseline and ORR. The proportional hazards and the logistic regression models were employed to assess the prognostic importance of race in predicting outcomes adjusting for established prognostic factors.

RESULTS

Of 8820 patients, 7528 (85%) were white, 500 (6%) were black, 424 were Asian (5%) and 368 (4%) had race unspecified. Median PFS were 8.3 [95% confidence interval (CI) 8.2-8.5], 8.2 (95% CI 7.4-8.8) and 8.3 (95% CI 7.6-8.8) months in white, black and Asian men, respectively. Median PSA PFS were 9.9 (95% CI 9.7-10.4), 8.5 (95% CI 8.0-10.3) and 11.1 (95% CI 9.9-12.5) months in white, black and Asian men, respectively.

CONCLUSIONS

We observed no differences in clinical outcomes by race and ethnic groups in men with mCRPC enrolled on these phase III clinical trials with DP.

Safety of BXCL701, a small molecule inhibitor of dipeptidyl peptidases (DPP), with pembrolizumab, (pembro, anti-PD-1) monoclonal antibody, in men with metastatic castration-resistant prostate cancer (mCRPC)

140

Background: BXCL701 (talabostat previously PT100) is an oral small molecule inhibitor of dipeptidyl peptidases (DPP) specifically DPP4, DPP8 and DPP9, which trigger macrophage cell death via pyroptosis resulting in proinflammatory stimulation of the innate immunity pathway. BXCL701 also inhibits fibroblast activation protein (FAP) releasing the FAP-mediated block of T-cell migration into the tumor. Expression of PD-L1 correlates with amplification of DPP8 and DPP9. In syngeneic animal models, significant tumor responses were observed when BXCL701 was used with checkpoint inhibition. Methods: A phase 1b, multicenter study was undertaken. Eligible patients (pts) had progressing mCRPC (PCWG3), at least 1 line of systemic therapy and ≤ 2 lines of cytotoxic chemotherapy for mCRPC, no prior anti-PD-1/PD-L1 or other T-cell directed anti-cancer therapy, and an ECOG PS of ≤ 2. Pts received fixed dose pembro (200mg IV q21 days) with escalating doses of BXCL701 (0.4mg and 0.6mg PO QD days 1-14 of 21-day cycles) using a 3 X 3 design. The key endpoints were safety and identification of the recommended phase 2 dose (RP2D) for the combination. Composite response (RECIST, PSA, CTC) was also assessed. Results: 3 pts were treated at the initial dose level for at least 4 cycles. All pts remain on treatment. No DLT or SAEs were reported. Grade 3 treatment related adverse events (TRAE) were limited to thrombocytopenia with transfusion in 1 pt. The only TRAE reported in more than one pt was hypocalcemia (2 pts). Safety assessment of BXCL701+pembro is ongoing at the final dose escalation cohort. As DPP9 is amplified in approximately 17% of treatment associated small cell/neuroendocrine prostate cancer (tSCNC) compared to 5% or less in the broader prostate cancer population, the Phase 2 portion of this study will be limited to patients with evidence of t-SCNC or de novo SCNC, an aggressive phenotype with poor outcomes. Conclusions: BXCL701 0.4mg QD on days 1 to 14 of 21-day cycle plus pembrolizumab 200 mg IV on day 1 every 21 days is safe in pts with mCRPC. The final dose escalation supporting RP2D will be presented. Clinical trial information: NCT03910660.

Efficacy of immune checkpoint inhibitors (ICIs) in rare histological variants of bladder cancer

502

Background: ICIs are effective agents in metastatic urothelial carcinoma in both platinum-refractory and frontline settings. Responses in patients (pts) with non-urothelial histological variants are not well defined. Methods: We undertook a retrospective analysis of pts with metastatic bladder cancer treated with ICI monotherapy. Pts were identified as having a variant histology if any non-urothelial component was present. Fisher’s exact test was used to assess differences in ORR by histology. Results: Between 12/2014 and 10/2019, 102 pts received ICI monotherapy, of whom 93 were evaluable for response and 33 had variant histology. Median age was 70 yrs, 66% were male, 50% received prior platinum-based chemotherapy. Most received pembrolizumab (66%) or atezolizumab (33%). ORR in the overall cohort was 26% (15% PR, 11% CR), with 12% having SD. Histology breakdown and responses are shown in Table. Although twice as many responses were seen in urothelial pts as in pts with variant histologies (ORR 31% vs 15%), this difference was non-significant (p = 0.14). Conclusions: In this large single-institution cohort, ORR in a heterogeneous population of bladder cancer pts was consistent with data previously reported in clinical trials. Pts with variant histologies had numerically lower responses relative to pure urothelial histology, but this difference was not statistically significant. Clinical benefit to ICIs was seen across multiple variant histologies suggesting potential efficacy in this patient population that should be confirmed prospectively.[Table: see text]

Differential expression of PSMA and 18F-fluciclovine transporter genes in metastatic castrate-resistant and treatment-emergent small cell/neuroendocrine prostate cancer

24

Background: 18F-fluciclovine (Axumin) PET/CT imaging is recommended by the NCCN in the setting of biochemical recurrence, while prostate-specific membrane antigen (PSMA) PET/CT is preferred by the EAU. The utility of these methods in the post-androgen deprivation therapy (ADT) setting however, is less defined. Our objective was to compare relative gene expression of the molecular targets of these imaging modalities— fluciclovine transporter genes (LAT1-4, ASCT1-2) and PSMA—in metastatic castrate resistant prostate cancer (mCRPC) and treatment-emergent small cell/neuroendocrine prostate cancer (t-SCNC). Methods: Genome-wide expression profiles of five mCRPC cohorts (Aggarwal, Grasso, Kumar, Beltran, Robinson, et al) were used to characterize relative expression of fluciclovine transporter (LAT1-4, ASC1-2) and PSMA (FOLH1) genes. 3 cohorts (Kumar, Beltran, Aggarwal) were enriched with t-SCNC tumors. The GSE35988 cohort included primary tumors and mCRPC. RNA expression profiling methods were consistent within cohorts. Results: 518 mCRPC specimens were included. In the GSE35988 cohort, PSMA expression was downregulated in mCRPC when compared to primary localized tumors (p=0.01). PSMA expression was further depressed in t-SCNC when compared with mCRPC (p<0.001). Of the fluciclovine transporter genes, LAT1 and LAT4 were overexpressed in mCRPC when compared to primary tumors, while ASC2 was less expressed (p<0.001). LAT1 was further overexpressed in t-SCNC when compared to mCRPC, while LAT2 was less expressed (p<0.001). PSMA expression was negatively correlated with LAT1 (p<0.001) but positively correlated with LAT2 (p=0.006). Other fluciclovine transporters were not correlated. Conclusions: Expression of PSMA and a subset of fluciclovine transporter genes are inversely correlated in mCRPC and t-SCNC. These findings suggest that fluciclovine-based imaging may play a role in castrate resistant states. Clinical comparison between PSMA- and fluciclovine-based imaging modalities in mCRPC and t-SCNC is warranted.

Treatment outcomes in metastatic prostate cancer patients with DNA damage repair mutations

187

Background: DNA damage repair mutations (DDM) are common in prostate cancer (PCa). Optimal treatment sequence and outcomes of androgen signaling inhibitors (ASIs) and chemotherapy in this population are unclear. Methods: A retrospective, single-institution study of patients (pts) with mPCa and DDM detected on next-generation sequencing between January 2016 and July 2019 was conducted. For pts with metastatic castration-resistant prostate cancer (mCRPC), chi-squared and Wilcoxon sum rank tests were used to compare PSA50 and Time to Next Treatment (TNT) among different treatment groups, respectively. Results: Among 70 pts with mPCa and DDM, the most common mutations were BRCA2 (24, 27%), ATM (20, 22%), CDK12 (19, 21%), and MLH1/MSH2/MSH6/PMS2 (10, 11%). Fifty-seven pts (81%) received systemic treatment for mCRPC and 68% received ≥3 mCRPC treatments. Among 57 pts with ≥1 mCRPC treatment, 19 (33%) received first abiraterone, and 18 (32%) first enzalutamide. There was a trend toward higher PSA50 (74% vs 47%, P=0.196) and longer TNT (55 vs 34 wk, P=0.286) with first abiraterone vs enzalutamide. Upon switching between ASIs, 0 of 10 pts had a PSA50 response. When given chemotherapy at any point during CRPC treatment, 16/27 (59%) pts had a PSA50 response to docetaxel alone and/or cabazitaxel alone, and 14/24 (58%) to carboplatin-based regimens. Conclusions: To our knowledge, this is the largest single-institution cohort providing real-world treatment data for pts with mPCa and DDM. In the frontline mCRPC setting, abiraterone had a trend suggesting increased activity over enzalutamide that was not statistically significant. Switching ASIs at progression produced no additional responses, suggesting cross-resistance. Responses to taxanes were similar to previously reported data in all-comers. Validation in a larger, prospective cohort is needed to confirm these preliminary findings.

Intermediate atypical carcinoma (IAC): A discrete subtype of metastatic castration-resistant prostate cancer (mCRPC) suggesting that treatment-associated small cell/neuroendocrine prostate cancer (t-SCNC) may evolve from mCRPC adenocarcinoma (adeno)—Results from the SU2C/PCF/AACR West Coast Prostate Cancer Dream Team (WCDT)

158

Background: A subset of mCRPC patients (pts) that develop resistance to next-gen androgen signaling inhibitors are subsequently found to harbor t-SCNC. We have undertaken a longitudinal prospective biopsy (bx) study to clinically and molecularly characterize these pts. Methods: Eligible pts underwent an image-guided mCRPC bx at one of 5 WCDT centers. Tissue was both frozen and formalin fixed/paraffin embedded (FFPE). FFPE tissue was used for targeted next generation sequencing (NGS) and independent pathologic review by 3 pathologists. Frozen specimens underwent laser capture micro-dissection prior to RNA sequencing (seq). Machine learning was used to derive histology-specific expression signatures. Linear Discriminant Analysis (LDA) was applied to the RNA seq data from the first 131 bx using 3 observed histologic subtypes as labels to test for an intermediate subtype. Results: Of 391 mCRPC metastasis (53% bone, 26% node, 12% liver, 9% other soft tissue), 295(75%) yielded cancer. Overall, 89% of the bx contained a single histologic subtype: pure adeno in 156(53%); pure t-SCNC in 35(12%). A novel morphologically distinct subtype, IAC, with features of both tSCNC and adeno was seen in 72(24%). Samples comprised of two subtypes made up 32(11%) of all bx. Overall, 50(17%) of bx had a t-SCNC component. TP53 and/or RB1 loss of function variants were significantly more frequent in t-SCNC. NGS revealed no difference between adeno and IAC. LDA classified IAC as intermediate between adeno and t-SCNC 93% of the time, across 100 bootstrap replicates, significantly better than the 33% expected by chance (p <10−17). Conclusions: Nearly half of mCRPC bx exhibit non-adeno features with t-SCNC found in 17%. IAC is a reproducible mCRPC histologic subtype found in 24% of bx, with a gene expression signature that is intermediate to adeno and t-SCNC, and targeted NGS results similar to adeno. Understanding the role of IAC in disease evolution and resistance is critical for improving outcomes in mCRPC. Clinical trial information: NCT02432001.

Characterization of PSMA and 18F-fluciclovine transporter gene expression in localized prostate cancer

295

Background: While 18F-fluciclovine PET/CT is approved in the US and recommended by the NCCN, prostate-specific membrane antigen (PSMA) PET/CT is more common in Europe/Australia and recommended by the EAU. Less is known about the biology of lesions detected by either modality. 18F-fluciclovine PET relies on radiotracer uptake by amino acid transporters LAT1-4 and ASCT1-2. PSMA PET is dependent on surface expression of PSMA. We compared relative expression of PSMA and fluciclovine transporter genes in radical prostatectomy (RP) samples to determine their distribution across subtypes and correlation with outcomes. Methods: Gene expression data of 19,102 RP samples were analyzed using the Affymetrix Human Exon 1.0 ST microarray. 1,135 patients had long term follow up. Associations between expression of PSMA and fluciclovine transporter genes (LAT1-4 and ASCT1-2) and pathologic variables, molecular subtypes, and clinical outcomes were conducted. Results: All fluciclovine transporter genes (LAT 1-4, ASCT1-2) were expressed at lower levels than PSMA (p <0.0001). PSMA expression was positively correlated with genomic risk score and pathologic Gleason score (p<0.0001), but LAT2-3 and ASCT2 were inversely correlated with genomic risk in primary tumors (p<0.0001) and less expressed in GS 9-10 tumors (p<0.0001). PSMA expression was associated with worse metastasis-free survival (MFS) (HR 1.45, p=0.001) and lymph node involvement (HR 2.14, p<0.0001). Expression of LAT2, LAT3, ASCT2 expression was associated with better MFS (HR 0.85, 0.63, 0.74, p<0.0001-0.04). After multivariable adjustment, PSMA expression remained independently prognostic of poorer MFS (HR 1.3, p=0.028). Luminal B subtype was notable for PSMA overexpression; Luminal A was enriched in ASCT2 and LAT2 (p<0.0001). PSMA expression did not correlate with ERG fusion prostate cancers, but LAT2, ASCT1, and ASCT2 were overexpressed in ERG fusion negative tumors (p<0.0001). Conclusions: PSMA expression is associated with more aggressive disease and poorer clinical outcomes than fluciclovine transporter genes in localized prostate cancer. Molecular subtypes of prostate cancer vary in PSMA and fluciclovine transporter gene expression.