Abstract P012: Genomic and clinical correlates of overall survival (OS) in men with newly diagnosed metastatic castration-sensitive prostate cancer (mCSPC) undergoing intensified androgen deprivation therapy (ADT)

Background: Despite recent advancements in systemic therapy in men with mCSPC, disease remains fatal. Identification of novel genomic and clinical correlates of survival in this setting remain a significant unmet need. Methods: Newly diagnosed mCSPC undergoing intensified ADT i.e., ADT plus docetaxel or novel hormonal therapy and available tumor comprehensive genomic profiling (CGP) were included in the analysis. CGP was performed by a CLIA certified Next Generation Sequencing panel (Foundation Medicine) and involved the following genes: FAS, KDM6A, MYC1, PTEN, RB1, TMPRSS2, and TP53. All variants of unknown significance were removed, and mutated genes present in ≥5 % patients were included. Cox proportional hazards was used to assess relationships between OS and multiple variables (age at diagnosis, Gleason score, baseline PSA, de-novo disease, volume of disease, presence of visceral metastases and presence of genetic aberrations on CGP). Results: 127 patients were eligible and included. Higher baseline PSA (HR 1.45, 95% CI 1.09-1.9, P=0.0097), presence of visceral metastases (HR 4.41, 95% CI 1.26-15.39, P=0.0199) and genomic aberrations in MYC1 (HR 5.23, 95% CI 1.05-26.04, P=0.0433) and RB1 (HR 32.72, 95% CI 5.35-200.2, P=0.0002) were significantly associated with inferior OS. High volume disease trended to associate with poor OS, but was not statistically significant (HR 1.63, 95% CI 0.56-4.71, P=0.367). PTEN loss and other genomic aberrations were not associated with OS. See Table. Conclusions: In this real-world patient population of men with mCSPC undergoing intensified ADT we identify clinical and genomic markers associated with poor OS. This study has limitations as expected in a retrospective analysis. These data, upon external validation, may aid with development of a risk stratification model, counseling of patients, treatment decision making in the clinic, as well as further drug development.

Citation Format: Nicolas Sayegh, Bennet Peterson, Roberto Nussenzveig, Adam Kessel, Taylor Ryan McFarland, Andrew Warren Hahn, Deepika Sirohi, Manish Kohli, Benjamin Louis Maughan, Umang Swami, Mark Yandell, Neeraj Agarwal. Genomic and clinical correlates of overall survival (OS) in men with newly diagnosed metastatic castration-sensitive prostate cancer (mCSPC) undergoing intensified androgen deprivation therapy (ADT) [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P012.

Landscape of circulating tumor DNA (ctDNA) abnormalities in advanced prostate cancer (aPCa): Distinctions in African American (AA) versus Caucasian (Ca) patients

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Background: AA have substantially higher prostate cancer incidence rates, are diagnosed at a younger age and with a more advanced stage as compared to Ca. However, after adjusting for known prognostic factors, AA have an increased overall survival. We hypothesized that these differences might be due to the underlying changes in the genomic landscape which can be revealed by liquid biopsy. Methods: Real world comprehensive genomic profiling of ctDNA from aPCa patients from two institutions. The first ctDNA results as reported by Guardant 360 panel (Redwood City, CA) were included. Association between genetic mutation and gene were tested using Barnard’s test. To account for multiple testing, we used Benjamini-Hochberg’s False Discovery Rate adjustment across all tests to determine thresholds for false discovery rates. Same analysis was performed using a Bayesian Network Machine learning approach. Results: Overall, 361 patients with aPCa (81 AA and 280 Ca) were included in the analysis. Pathogenic genomic alterations were found in 87.0% of the cases, more frequently TP53 (42.4%), AR (34.1%), PIK3CA (13.9%), BRAF (12.7%), NF1 (10.8%) and MYC (10.0%). Targetable alterations of interest included DNA repair genes [BRCA 2 (7.8%), BRCA 1 (4.4%), ATM (6.4%), CDK12 (2.2%)], PIK3CA/mTOR/AKT (19.1%), PTEN (3.3%) and NTRK (1.9%). MSI-high was found in 4 patients. AA as compared to Ca had a significantly higher prevalence of CDK12 (20.7% vs. 3.8%, p=0.016) and GNA11 mutations (3.7% vs. 0.4%, p=0.0225). BayesNet analysis also supported these results (table). Conclusions: In this dataset, liquid biopsy of ctDNA was useful for genetic characterization of aPCa and reveal differences in the molecular phenotype of AA and Ca in aPCa with potential clinical implications. These findings support ongoing research on the clinical utility of non-invasive genotyping and therapeutic response monitoring with a focus on AA population. [Table: see text]

Combination therapy with avelumab (Ave) and cabozantinib (Cabo) in patients (pts) with newly diagnosed metastatic clear cell renal cell carcinoma (mccRCC)

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Background: Immune therapy combinations are now standard first-line therapy for pts with mccRCC. Cabo modulates key components of the immune system such as decreasing regulatory T-cells and increasing T-effector cell populations and is approved for treatment of mRCC. We hypothesize that Ave + Cabo will be safe and show clinical activity in mccRCC. Methods: Prospective phase I clinical trial using a 3+3 design with three planned dose cohorts: Cabo 20mg/day, 40mg/day and 60mg/day + Ave (10mg/kg q2weeks) in each arm. The primary endpoint was safety and identification of the recommended phase II dose (RP2D). Key secondary endpoints included objective response rate (ORR) and radiographic progression free survival (PFS). No dose modifications were allowed for Ave but dose delays were permitted. Dose reductions were allowed for Cabo. There were an additional 3 patients included in the final dose cohort as a confirmation of the RP2D. RECIST 1.1 was used to determine ORR. Treatment beyond progression was allowed. Results: Twelve patients with newly diagnosed mccRCC were enrolled from 08/2018 through 03/2020. Three patients were enrolled into the 20 and 40mg cohorts each, six patients enrolled in the 60mg cohort. IMDC risk: favorable 4 patients, intermediate 6 patients, poor 2 patients. No dose limiting toxicities were observed in any cohort. Only one SAE related to study treatment was observed, thromboembolism, after the DLT period. Immune related adverse events (irAE) occurred in six patients (50%) and included hypothyroidism, colitis, nephritis, allergic rhinitis and rash. Six patients required dose reductions of cabozantinib after the DLT period: one in the 40mg cohort and five in 60mg cohort, most frequently due to oral mucositis and hand foot syndrome. One patient discontinued Ave due to irAE (nephritis). No patients discontinued Cabo due to toxicity. The ORR was 33% (all PR). The clinical benefit rate (CR+PR+SD) was ~ 92%. One patient experienced PD on the first scan and then continued on the protocol treatment without further progression at the time of this report (follow up to date ~ 7 months). Seven of 12 pts are still on protocol treatment. Conclusions: Ave + Cabo in mccRCC is safe and preliminarily efficacious. Even though the DLT was not met in any of the cohorts, based on dose reduction required in 5 of 6 pts in the Cabo 60 mg cohort after the DLT period, the recommended RP2D dose for the combination is Cabo 40mg/day and Ave 10mg/kg q2 weeks. Safety and efficacy data will be elaborated in the meeting. * NA & BLM: equal contribution Clinical trial information: NCT03200587 .

Comprehensive genomic profiling of matched primary prostate cancer tissue and cell-free DNA (cfDNA) to assess ontogeny of BRCA1/BRCA2 mutations

166

Background: Both olaparib and rucaparib have recently been approved for the treatment of metastatic castration resistant prostate cancer (mCRPC) with BRCA1/2 mutations (BRCAm). In the PROFOUND trial, 36.9% of men had either no tissue or tissue that was inadequate for genomic profiling (PMID: 32343890). A recent report suggests BRCAm may be an early event in the evolution of prostate cancer (PMID: 29662167). This suggests comprehensive genomic profiling (CGP) of primary prostate tissue may suffice to guide treatment selection, even years after tissue collection. Herein, we investigate the ontogeny of BRCAm by comparing CGP of matched primary prostate cancer tissue to CGP of cfDNA. Methods: Eligibility criteria included men diagnosed with metastatic prostate cancer that had matched CGP of both primary prostate cancer tissue and cfDNA. Genomic profiling was performed by CLIA certified laboratories. Only somatic mutations detectable by both platforms were used for concordance analysis. Results: We identified 198 patients that had matched CGP of primary prostate tissue and cfDNA. Thirteen men had a pathogenic BRCAm in at least one test. Of these 13 positive test for BRCAm, 2 were rearrangements, 1 copy number loss, and 5 were germline mutations. Both platforms tend to filter out germline alterations therefore, they were not included in the estimation of concordance. Overall somatic BRCAm concordance between primary prostate tissue and cfDNA was 196/198 (98%). Notably, no new BRCAm were identified in cfDNA with a median difference of 23.62 (0.1 - 232.2) months between prostate cancer tissue and cfDNA collection. Conclusions: There were no BRCAm detected only in cfDNA, suggesting that BRCAm is an early event in the ontogeny of prostate cancer. Based on this, it is unlikely that delaying sequencing would benefit patients with advanced prostate cancer. In the event that tissue is unavailable or inadequate for CGP, profiling of cfDNA is a valuable alternative for detection of BRCAm.

Randomized phase II trial of radium-223 (RA) plus enzalutamide (EZ) versus EZ alone in metastatic castration-refractory prostate cancer (mCRPC): Final efficacy and safety results

135

Background: We previously reported that treatment with EZ+RA was associated with a decline in serum bone metabolism markers (BMM), which correlated with improved outcomes compared to EZ alone (Agarwal N et al, Clinical Cancer Research, 2020, PMID 31937614). Here we report the final efficacy and safety results for this trial. Methods: In this phase 2 trial (NCT02199197), patients (pts) with progressive mCRPC were treated with EZ (160 mg daily) ±RA (standard dose of 55 kBq/kg IV Q4 weeks x 6), until disease progression or unacceptable toxicities. Primary objectives of change in bone markers and safety have been reported previously. Secondary objectives included comparison of PSA progression free survival (PFS), overall survival (OS), and long term safety in all pts receiving RA+EZ vs EZ alone. Post hoc analysis included comparison of PSA-PFS2 (defined as time from start of protocol therapy to PSA progression on subsequent therapy or death whichever occurred earlier), time to subsequent/next therapy (TTNT), and long term safety. Survival analysis and log-rank tests was performed using the R statistical package v.4.0.2 ( https://www.r-project.org ). Statistical significance was defined as P<0.05. Results: Between 08/2014 and 11/2017, 47 pts were eligible and enrolled. Median follow up was 22 months (range 3.2-71.5). Thirty-five pts received RA+EZ and 12 pts received EZ alone. Receipt of prior abiraterone was allowed and was balanced between two groups: 60% in RA+EZ vs. 64% in EZ pts. Final efficacy results: TTNT, PSA-PFS2 were significantly improved in the RA+EZ pts over EZ alone pts, and all other efficacy parameters were numerically improved in RA+EZ pts (Table). Final safety results: none of the 12 EZ alone pts had any fracture; two of 35 RA+EZ pts were found to have incidental grade 1 asymptomatic fracture at the site of bone metastasis on routine imaging, at 15 and 31 months respectively after the last dose of RA, and did not require any intervention. No patients developed bone marrow disorders during the follow-up period. Efficacy and safety data will be elaborated during the meeting. Conclusions: In our study, EZ+RA resulted in significant long-term clinical benefit over EZ alone in pts with mCRPC without compromising safety. * NA&BLM; equal contribution. Clinical trial information: NCT02199197. [Table: see text]

Illustration of temporal evolution in patients with metastatic renal cell carcinoma (mRCC) using both circulating tumor DNA (ctDNA) and tissue-based genomic data

347

Background: We have previously demonstrated the feasibility of ctDNA assessment in mRCC and preliminarily showed agreement between ctDNA and tissue-based genomic findings (Zengin et al ESMO 2020). Our data suggested that the degree of agreement is dependent upon the temporal separation of blood and tissue samples. We sought to further explore this temporal impact in a separate validation cohort. Methods: Patients (pts) with mRCC who underwent ctDNA genomic profiling were identified. ctDNA analysis was performed using a CLIA-certified 73-74 gene panel (Guardant360). From this cohort we identified a subset of pts who also underwent tissue-based genomic profiling using either a whole exome sequencing platform (GemExtra [TGen, Phoenix, AZ]) or a targeted next generation sequencing platform (Foundation Medicine [Cambridge, MA] or Tempus [Chicago, IL]). Only alterations covered by both assays were included for the current analysis. The difference in the proportion of alterations detected on tissue and ctDNA was compared between these cohorts and at a 6-mo landmark using the χ2 test. Results: In total, ctDNA and tissue based genomic profiling was assessed in 112 pts (M:F, 81:31); with most common histology was clear cell (85.7%). Median time between ctDNA and tissue assessments was 9.8 months (IQR 1.15-23.7). When examining paired samples in which >1 ctDNA alteration was detected, 32% (43/133) of alterations detected on tissue were also detected in ctDNA. This proportion increased to 43% (29/67) when samples collected within 6 months of each other, and was 51% (28/55) in samples collected within 3 months of each other. There was no significant difference in the frequency of shared mutations between the cohorts (P=0.09; Table). Conclusions: Our study confirms that ctDNA and tissue-based genomic profiling continue to provide consistently high levels of agreement. Notably, the percentage of samples with ≥1 ctDNA alteration detected was significantly lower in both cohorts compared to previous studies in RCC. More shared alterations were found on ctDNA when both ctDNA and tissue-based assessment were obtained at closer intervals. [Table: see text]

Association of circulating tumor cells (CTC) with survival outcomes in patients (pts) with metastatic castration-sensitive prostate cancer (mCSPC) in a real-world cohort

59

Background: In mCSPC, baseline CTC counts have been shown to correlate with PSA responses and progression free survival (PFS) in small studies in the context of androgen deprivation therapy (ADT) without modern intensification with docetaxel or novel hormonal therapy. Similar correlation of CTC count with PSA responses and PFS was recently reported from an ongoing phase 3 trial in mCSPC setting (SWOG1216) without reporting the association in the context of ADT intensification. Furthermore, none of these studies correlated CTCs with overall survival (OS). Herein we evaluated whether CTCs were associated with outcomes including OS in a real world mCPSC population treated with intensified as well as non-intensified ADT. Methods: Eligibility criteria: new mCSPC receiving ADT with or without intensification and enumeration of baseline CTCs by FDA cleared Cell Search CTC assay. The relationship between CTC counts (categorized as: 0, 1-4, and ≥5/7.5 ml) and both PFS and OS was assessed in the context of Cox proportional hazards models, both unadjusted and adjusted for age, Gleason, PSA at ADT initiation, de novo vs. non-de novo status, and ADT intensification vs. non-intensification therapy. Results: Overall 99 pts were identified. Baseline characteristics are summarized in Table. In unadjusted analyses, CTC counts of ≥5 as compared to 0 were strongly associated with inferior PFS (hazard ratio [HR] 3.38, 95% CI 1.85-6.18; p < 0.001) and OS (HR 4.44 95% CI 1.63-12.10; p = 0.004). In multivariate analyses, CTC counts of ≥5 as compared to 0 continued to be associated with inferior PFS (HR 5.49, 95% CI 2.64-11.43; p < 0.001) and OS (HR 4.00, 95% CI 1.31-12.23; p = 0.015). Within the ADT intensification subgroup also, high CTC counts were associated with poor PFS and OS. For PFS, the univariate HR for CTC ≥5 vs. 0 was 4.87 (95% CI 1.66-14.30; p = 0.004) and multivariate HR for CTC ≥5 vs. 0 was 7.43 (95% CI 1.92-28.82; p = 0.004). For OS, the univariate HR for CTC ≥5 vs. 0 was 15.88 (95% CI 1.93-130.58; p = 0.010) and multivariate HR for CTC ≥5 vs. 0 was 24.86 (95% CI 2.03-304.45; p = 0.012). Conclusions: To best of our knowledge this is the first study to show that high baseline CTC counts are strongly associated with inferior PFS as well as OS in pts with newly diagnosed mCSPC, even in those who received intensified ADT therapy. Identifying these pts at highest risk of progression and death can help with counselling and prognostication in clinics as well as design and enrollment in future clinical trials. [Table: see text]

Phase II study of the oral hypoxia-inducible factor 2α (HIF-2α) inhibitor MK-6482 for Von Hippel-Lindau (VHL) disease-associated clear cell renal cell carcinoma (ccRCC)

333

Background: Patients (pts) with VHL disease are at risk of developing benign and malignant tumors, including ccRCC, pancreatic lesions tumors, CNS hemangioblastomas, and retinal lesions. Inactivation of VHL leads to stabilization of HIF-2α, which drives tumor growth. In a phase 1/2 study, MK-6482, a potent, selective, oral small molecule HIF-2α inhibitor, demonstrated favorable safety and antitumor activity in advanced ccRCC. We present results of the open-label phase 2 study of MK-6482 for VHL disease–associated ccRCC (NCT03401788). Methods: Adults with germline VHL alterations, measurable, localized/non-metastatic ccRCC, no prior systemic anticancer therapy, and ECOG PS 0/1 received MK-6482 120 mg once daily until progression, intolerable toxicity, or decision to withdraw. Primary end point: ORR of VHL-associated ccRCC tumors per RECIST v1.1 by independent review committee (IRC). Secondary end points: DOR, time to response (TTR), PFS, and safety. Results: As of June 1, 2020, 61 pts enrolled. The majority (82%) of pts had ECOG PS 0, and median number of prior surgeries per pt was 5 (range, 1-15). Lesions outside the kidney (non-RCC tumors) evaluable by IRC included pancreatic lesions (100%) and CNS hemangioblastomas (70%). Median duration of treatment was 68 wk (range, 8-105), and 92% of pts remain on therapy. There were 22 confirmed responses (ORR, 36% [95% CI, 24%-49%]) and 7 (11%) unconfirmed (documented at 1 time point, to be confirmed at subsequent time point) responses; all PRs. In pts with confirmed PR, median DOR was not reached (range, 12-62 wk) and median TTR was 31 wk (range, 12-61); 14 (64%) pts had response duration of ≥26 wk. 56 pts (92%) had any decrease in size of target lesions. PFS rate at 52 wk was 98% (95% CI, 89%-100%). Overall, pretreatment median linear growth rate of ccRCC tumors was +3.6 mm/y (range, −3.4 to +33.1), compared with −4.5 mm/y (range, −12.8 to +5.1) while on treatment. For non-RCC tumors, ORR in pancreatic lesions was 64% (39/61, including 4 CRs) and in CNS hemangioblastomas was 30% (13/43, including 5 CRs). Median (range) TTR was 35 wk (11-60) and 12 wk (10-60) for pancreatic lesions and CNS hemangioblastomas, respectively. 11/16 (69%) pts with evaluable retinal lesions at baseline showed improvement. Of those 16 pts, 29 eyes were followed for retinal lesions; 16 eyes (55%) showed improvement, 12 (41%) remained stable, and no follow-up evaluation was available for 1 (3%) eye. Treatment-related AEs (TRAEs) occurred in 98% of pts, none grade 4/5. Most common TRAE was anemia (87%), considered to be an on-target toxicity. One pt discontinued treatment due to a TRAE (grade 1 dizziness). As of data cutoff, 1 pt (2%) required surgery for ccRCC tumors after treatment. Conclusions: MK-6482 is an active and well-tolerated therapy for VHL disease–associated ccRCC, pancreatic lesions, as well as CNS and retinal hemangioblastomas. Clinical trial information: NCT03401788 .

Association of SPOP Mutations with Outcomes in Men with De Novo Metastatic Castration-sensitive Prostate Cancer

Recently, mutations in speckle-type pox virus and zinc finger protein (SPOP) gene (mutant SPOP [mtSPOP]) have been associated with improved outcomes to abiraterone in the castration-resistant setting. We hypothesized that mtSPOP would be associated with improved outcomes to systemic therapy in men with de novo metastatic castration-sensitive prostate cancer (d-mCSPC). Retrospective data of newly diagnosed d-mCSPC patients were collected from four institutions. Eligibility criteria included standard androgen deprivation therapy without intensification, and SPOP mutational status (mtSPOP or wild-type SPOP [wtSPOP]) determination by targeted next-generation sequencing from tumor biopsies. A total of 121 men (25 mtSPOP [21%] and 96 wtSPOP [79%]) were included. After adjusting for covariates, mtSPOP was significantly associated with better median progression-free survival (35 vs 13 mo; adjusted hazard ratio [HR] 0.47; p =  0.016) and overall survival (97 vs 69 mo; adjusted HR 0.32; p =  0.027), with similar HR and p value on the univariate analysis. These findings, upon external validation, may assist with counseling and prognostication in the clinic, and inform the design of future clinical trials in this setting. PATIENT SUMMARY: : Presence of tumor mutation in speckle-type pox virus and zinc finger protein (SPOP) gene was associated with improved survival outcomes in men with de novo metastatic castration-sensitive prostate cancer receiving standard androgen deprivation therapy.

Overall survival (OS) with docetaxel (D) vs novel hormonal therapy (NHT) with abiraterone (A) or enzalutamide (E) after a prior NHT in patients (Pts) with metastatic prostate cancer (mPC): Results from a real-world dataset

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Background: NHT (A and E) are approved first-line (1L) treatment (Rx) for mPC. After progression on NHT, Rx include either alternate NHT or D. However, OS from a randomized trial comparing NHT vs D after progression on 1L NHT has not been reported. Methods: Pts data were extracted from the Flatiron Health EHR-derived de-identified database. Inclusion: diagnosis of mPC; 1L Rx with single agent A or E only, single-agent Rx with alternate NHT (E or A) or D in second line (2L). Exclusion: > 180 days between date of diagnosis of mPC and date of next visit to ensure Pts were actively engaged in care at data-providing site; Rx with NHT in non-metastatic setting, any prior exposure to D. OS was compared using Cox proportional hazards model stratified by Rx propensity score. Each Pts’ probability of receiving D (rather than NHT) was modeled via a random forest based on Pts and disease characteristics which may drive treatment selection. These included pre-2L Rx ECOG scores, PSA, LDH, ALPH, Hb, age, ICD codes for liver metastasis, diabetes, neuropathy, and heart failure; insurance payer, year of start of 2L Rx, time on 1 L NHT, Gleason score, PSA at the original diagnosis of mPC. Subgroup analyses included 1L Rx duration < 12 mos. Results: 1165 Pts between 2/5/2013 to 9/27/2019 were eligible. Median follow up 8 mos (range 0.1-64.5). Median OS after 1L A was higher with E as compared to D (15.7 vs. 9.4 mos). Median OS after 1L E was higher with A as compared to D (13.3 vs. 9.7 mos) (table). Propensity distributions were overlapping among Rx arms and showed only modest imbalance. In 2L, D had a worse adjusted hazard ratio of 1.29 and 1.35 as compared to E and A respectively (p < 0.05). Similar results were seen with 1L Rx duration of < 12 mos (p < 0.05). Conclusions: These hypothesis-generating data provide real-world OS estimates with 2L D & NHT in mPC. In propensity-stratified analyses, mPC Pts who progressed on NHT had a worse OS with 2L D as compared to alternate NHT. Results were consistent in unadjusted analysis & subgroup analyses of 1L Rx < 12 mos. Results are subject to residual confounding and missingness. After prospective validation these data may aid in Rx sequencing, Pts counselling, and design of future clinical trials in this setting. [Table: see text]

Comparative effectiveness of second-line (2L) single-agent atezolizumab (A), nivolumab (N), and pembrolizumab (P) in patients (Pts) with locally advanced or metastatic urothelial cancer (aUC) who progressed on platinum-based systemic chemotherapy (plat-chemo): Results from a real-world dataset

5032

Background: Five PD-1/L1 inhibitors (PDi) are approved for 2L therapy (Rx) for aUC after progression on plat-chemo, but none compared with each other in randomized trials. Here, we assessed comparative effectiveness of 2L PDi in real-world setting. Methods: Pt level data of Pts with aUC were extracted from Flatiron Health EHR-derived de-identified database. Inclusion criteria: 1L Rx with plat-chemo; receipt of single agent PDi in 2L; initiation of 2L PDi 6 mos before data-cut off. Exclusion criteria: >90 days from diagnosis to date of next visit to ensure active engagement of Pts with data providing site; initiation of 2L after 7/31/2016 to ensure uptake of PDi for aUC. OS was compared from the date of initiation of 2L Rx. Comparative effectiveness was examined by Cox proportional hazards model, stratified by treatment propensity score. Each Pts’ propensity of receiving each 2L PDi was modeled via a random forest based on Pt and disease characteristics potentially driving Rx selection for a PDi (gender, smoking status, race/ethnicity, relapsed vs de novo disease, time between 1L & 2L Rx, cis vs carboplatin in 1L; year of Rx with PDi & following characteristics before 2L Rx: ECOG, Hb, age, ICD codes for liver or CNS mets, albumin & PD-L1 status when available). Results: 703 Pts with aUC who initiated 2L Rx between 8/1/2016 to 10/31/2019 were eligible. 2L Rx were A (n=322), N (n=127) & P (n=254). Durvalumab & avelumab were excluded due to low utilization in this dataset. Median follow up from 2L initiation was 4.8 mos. Median OS (mos; 95% CI) with A (6.4 mos; 5-8.7), N (8 mos; 6.3-11.3) and P (8.5 mos; 6.1-11.6) were similar (propensity stratified log rank p=0.19; simple log-rank p=0.34). Over time proportion of Pts receiving 2L A decreased, P increased & N increased then decreased (p<0.001). Propensity stratified comparative effectiveness estimates are below. Conclusions: In this real-world cohort of Pts with aUC, OS with 2L Rx with A, N, & P were similar on both univariate and propensity stratified analyses. These results agree with prior trial level meta-analysis (PMID 31200951). Strength of this analysis includes large Pt level data from a real world cohort. Limitations include retrospective nature of this study. [Table: see text]

Phase II study of the oral HIF-2α inhibitor MK-6482 for Von Hippel-Lindau disease–associated renal cell carcinoma

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Background: Patients (pts) with Von Hippel-Lindau disease (VHL) are at risk for several cancers, including clear cell renal cell carcinoma (ccRCC). Inactivation of VHL results in constitutive activation of the HIF-2α transcription factor, which drives tumor growth. MK-6482, a potent, selective, small molecule HIF-2α inhibitor, has shown favorable safety and antitumor activity in a phase 1/2 study. We present initial results of the open-label phase 2 study of MK-6482 for treatment of VHL-associated ccRCC (NCT03401788). Methods: Adult pts with a pathogenic germline VHL variation, measurable localized/nonmetastatic ccRCC, no prior systemic anticancer therapy, and ECOG PS of 0/1 received MK-6482 120 mg orally once daily until progression, intolerable toxicity, or investigator/pt decision to withdraw. Primary end point was ORR of VHL-associated ccRCC tumors per RECIST v1.1 by independent radiology review. Secondary end points were DOR, time to response (TTR), PFS, and safety and tolerability. Results: As of December 6, 2019, 61 pts were enrolled; median (range) age was 41 years (19-66) and most pts were male (52.5%) and had ECOG PS of 0 (82.0%). The most common lesions outside the kidney (non-RCC tumors) were CNS hemangioblastomas (80.3%) and pancreatic lesions (50.8%). Median (range) duration of treatment was 9.9 mo (1.9-18.2) and 95.1% of pts remain on therapy. Three pts discontinued (AE, n = 1; death [fentanyl toxicity], n = 1; pt decision, n = 1). There were 17 confirmed responses (ORR, 27.9% [95% CI, 17.1-40.8%]) and 8 (13.1%) unconfirmed (documented at 1 timepoint and to be confirmed at subsequent timepoint) responses; all responses were PRs. Of 61 pts, 53 (86.9%) had decrease in size of target lesions. In 17 pts with confirmed response, median (range) DOR was not reached (2.1-9.0 mo) and median (range) TTR was 5.5 mo (2.7-14.0). Responses were also observed in CNS, retinal, and pancreatic lesions. Median PFS was not reached; 12-mo PFS rate was 98.3%. Treatment-related AEs (TRAEs) occurred in 96.7% of pts, mostly grade 1 (44.3%) or grade 2 (42.6%) and primarily (≥20%) anemia (83.6%; considered an on-target-toxicity), fatigue (49.2%), and dizziness (21.3%). Grade 3 TRAEs occurred in 9.8% of pts, primarily fatigue (4.9%) and anemia (3.3%). There were no grade 4 or 5 TRAEs. One pt discontinued because of a TRAE (dizziness). Conclusions: MK-6482 showed promising efficacy and tolerability in pts with VHL-associated ccRCC and responses in other VHL-related lesions. These data support further investigation of MK-6482 in VHL disease. Clinical trial information: NCT03401788 .

Genomic alterations associated with the progression from castration-sensitive to castration-resistant metastatic prostate cancer based on machine learning analysis of cell-free DNA genomic profile

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Background: Metastatic castration-sensitive prostate cancer (mCSPC) eventually progresses to metastatic castration-resistant prostate cancer (mCRPC), which has few treatment options and carries a poor prognosis. We hypothesize that there are specific genomic alterations (GAs) associated with the progression from mCSPC to mCRPC. Methods: Patients (Pts) with mCSPC and mCRPC undergoing next-generation sequencing of cell-free DNA by a CLIA certified lab (G360, Guardant Health Inc., Redwood City, CA) as a part of routine care were retrospectively identified. Principal components analysis, an unsupervised ML algorithm, was used for data exploration and visualization. A combination of feature selection and supervised machine learning classification algorithms were used to identify genes associated with mCRPC. Gene Ontology enrichment analysis was used to identify pathways enriched for mCRPC-associated GAs. Patterns of mCRPC-associated GAs at a gene- and pathway-level were identified by Bayesian networks fitted using an exact structure learning algorithm. Results: 154 Pts with mCSPC and 187 Pts with mCRPC were included. A set of 16 GAs that robustly distinguished mCRPC from mCSPC (PPV = 94%, specificity = 91%) using supervised machine learning algorithms. These GAs, primarily amplifications, corresponded to AR, MAPK signaling, PI3K signaling, G1/S cell cycle, and receptor tyrosine kinases (RTKs). Positive statistical dependencies were observed between genes in these pathways. At a pathway-level, the presence of G1/S GAs in mCRPC samples increased the likelihood of harboring GAs in RTK, MAPK, and PI3K signaling. Limitations: The retrospective nature of our study means that unknown exposures could act as confounding variables, however this is representative of real-world clinical settings. Although the strength of this study is inclusion of clinically annotated patient samples, the limitation is that patients with mCSPC and mCRPC were unmatched. Conclusions: These results provide evidence that progression from mCSPC to mCRPC is associated with stereotyped concomitant gain-of-function in the RTK, PI3K, MAPK, and G1/S pathways in addition to AR. Upon external validation, these hypothesis generating data may warrant further investigation into combinatorial therapies that target these pathways.

Cabozantinib in combination with atezolizumab in patients with metastatic castration-resistant prostate cancer: Results of cohort 6 of the COSMIC-021 study

5564

Background: Cabozantinib (C) may enhance response to immune checkpoint inhibitors (ICIs) by promoting an immune-permissive microenvironment and has shown encouraging activity in combination with ICIs in tumor types including RCC and HCC. C and atezolizumab (A) have shown low objective response rates as monotherapy in metastatic castration-resistant prostate cancer (mCRPC) (Smith JCO 2012; Kim JCO 2018). COSMIC-021 (NCT03170960), a multinational phase 1b study, is evaluating the combination of C + A in various solid tumors. We report results for Cohort 6 in mCRPC. Methods: Eligible patients (pts) were required to have radiographic progression in soft tissue after enzalutamide and/or abiraterone, measurable disease, and an ECOG PS of 0 or 1. Prior chemotherapy for mCSPC was permitted. Pts received C 40 mg PO QD and A 1200 mg IV Q3W. CT/MRI scans were performed Q6W for the first year and Q12W thereafter. The primary endpoint is ORR per RECIST 1.1. Other endpoints include safety, ORR per irRECIST, duration of response (DOR), PFS, and OS. Results are presented for the first 44 pts enrolled. Results: Median follow-up as of Dec 20, 2019 was 12.6 mo (range 5, 20) for the 44 mCRPC pts. Median age was 70 y (range 49, 90), 50% had ECOG PS 1, 34% had visceral metastases, and 61% had extrapelvic lymph node metastases. 27% had prior docetaxel and 52% had 2 prior novel hormonal therapies. The most common any grade treatment-related adverse events (TRAEs) were fatigue (50%), nausea (43%), decreased appetite (39%), diarrhea (39%), dysgeusia (34%), and PPE (32%). One grade 5 TRAE of dehydration was reported in a 90 y/o. Median duration of treatment was 6.3 mo. ORR per RECIST 1.1 among all 44 pts was 32% (2 CRs [4.5%] and 12 PRs [27%]); 21 (48%) pts had SD resulting in a disease control rate of 80% in all pts. One pt with PD per RECIST 1.1 had an irPR per irRECIST. ORR per RECIST 1.1 was 33% in 36 pts with high-risk disease (visceral and/or extrapelvic lymph node metastases). Median DOR for all pts with response per RECIST 1.1 was 8.3 mo (range 2.8, 9.8+). 17 (50%) of 34 pts with post-baseline PSA evaluation had a decrease in PSA. In 12 responders with post-baseline PSA evaluation, 8 (67%) had a PSA decrease ≥50%. Tumor PD-L1 expression will also be reported. Conclusions: The combination of C + A had a tolerable safety profile and demonstrated clinically meaningful activity with durable responses in men with mCRPC. Given the encouraging activity in these pts, especially in those with high-risk disease, further evaluation of C + A in men with mCRPC is being pursued. Clinical trial information: NCT03170960 .

Optimized management of nivolumab (Nivo) and ipilimumab (Ipi) in advanced renal cell carcinoma (RCC): A response-based phase II study (OMNIVORE)

5005

Background: Nivo + Ipi is an established first-line treatment (tx) for advanced RCC. We hypothesized that the addition of CTLA-4 blockade may not be required for all patients (pts). Furthermore, the optimal duration of Nivo maintenance in responding pts is unknown. In this phase II response-adaptive trial, we investigate the sequential addition of 2 doses of Ipi to induce response in Nivo non-responders (NR) and duration of Nivo in responding pts (NCT03203473). Methods: We enrolled pts with advanced RCC with no prior checkpoint inhibitor exposure. All pts received Nivo alone with subsequent arm allocation based on RECISTv1.1 response within 6 months (mos) of tx. Pts with a confirmed partial response (PR) or complete response (CR) within 6 months (mos) discontinued Nivo and were observed (Arm A). Arm A pts reinitiated Nivo if they developed progressive disease (PD); Ipi was added to Nivo if PD persisted or recurred. Pts with stable disease (SD) or PD after no more than 6 mos of Nivo alone received 2 doses of Ipi (Arm B). The primary endpoints were the proportion with PR/CR at 1-year (yr) after Nivo discontinuation (Arm A) and proportion of Nivo NR who convert to PR/CR after adding Ipi (Arm B). Results: 83 pts initiated tx of whom 99% had ECOG 0-1, 96% clear cell RCC, 51% tx-naïve, and 69% IMDC intermediate/poor risk. Median follow-up was 17.0 mos. 15 pts were not allocated to an arm [7 withdrew for PD, 7 withdrew for toxicity, 1 still on tx with unconfirmed PR (uPR)]. At 6 mos, induction Nivo resulted in a confirmed PR in 11% of pts (n=9/83): 12% (n=5/42) tx-naïve, 10% (4/41) prior tx, 8% (n=1/13) favorable risk, 11% (n=8/70) intermediate/poor risk (Table). 11 pts (13%: 9 PR, 1 uPR, 1 SD) were allocated to Arm A, of whom 5 (45%, 90% CI 20-73%) remained off Nivo at ≥ 1 yr. Of 57 pts (69%) allocated to Arm B, 2 pts converted to a PR (4%, 90% CI 1-11%), both of whom had prior tx and PD as best response to Nivo alone. Grade 3-4 treatment related adverse events (TrAE) occurred in 7% (n=6/83) on induction Nivo and in 23% (n=13/57) on Arm B (Nivo + Ipi). Conclusions: We cannot currently recommend a strategy of Nivo followed by response-based addition of Ipi due to the absence of CR and low PR/CR conversion rate (4%). Though a subset of pts treated with Nivo alone can maintain durable responses off tx at 1-yr, early Nivo discontinuation in the absence of toxicity cannot currently be recommended. Investigation into biomarkers to guide tx is ongoing. Clinical trial information: NCT03203473 . [Table: see text]

Cabozantinib (C) in combination with atezolizumab (A) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC): Results of Cohort 6 of the COSMIC-021 Study

139

Background: C may enhance response to immune checkpoint inhibitors by promoting an immune-permissive microenvironment. COSMIC-021 (NCT03170960), a multinational phase 1b study, is evaluating the combination of C with A in various solid tumors. We report interim results from Cohort 6 in mCRPC. Methods: Eligible pts were required to have radiographic progression in soft tissue after enzalutamide and/or abiraterone, measurable disease, and an ECOG PS of 0 or 1. Prior chemotherapy for mCSPC was permitted. Pts received C 40 mg PO qd and A 1200 mg IV q3w. CT/MRI scans were performed q6w for 52w and q12w thereafter. Bone scans were performed q12w. The primary endpoint is ORR per RECIST 1.1. Other endpoints include safety, ORR per irRECIST, duration of response (DOR), PFS, and OS. Results: As of Oct 2019, 44 mCRPC pts were enrolled with a median follow-up of 10.6 mo (range 3.4+, 17.9). Median age was 70 y (range 49, 90), 50% had ECOG PS 1, 34% had visceral metastases, and 61% had extrapelvic lymph node metastases. 27% of pts had prior docetaxel and 52% had ≥2 prior novel hormonal therapies. The most common any grade TEAEs were fatigue (57%), nausea (48%), decreased appetite (45%), diarrhea (39%), PPE (32%), and vomiting (32%). One Grade 5 TRAE of dehydration was reported in a 90 y/o. Median duration of treatment was 5.3 mo. The ORR per RECIST 1.1 among all pts was 32% (2 CRs [4.5%] and 12 PRs [27%]); 21 (48%) pts had SD giving a disease control rate of 80% in all pts. One pt with initial PD per RECIST 1.1 had an irPR per irRECIST. ORR per RECIST 1.1 was 33% in 36 pts with high-risk clinical features (visceral and/or extrapelvic lymph node metastases). Median DOR for all pts with response per RECIST 1.1 was 8.3 mo (range 1.38+, 9.76+). In 12 responders with at least 1 post-baseline PSA evaluation, 8 (67%) had a PSA decline ≥50%. Conclusions: The combination of C+A had a tolerable safety profile and demonstrated clinically meaningful activity with durable responses in men with mCRPC. Given the encouraging activity in these pts, especially in those with visceral and/or extra pelvic lymph node metastases, further evaluation of C+A in men with mCRPC is being pursued. Clinical trial information: NCT03170960.

Genomic alterations in visceral versus nonvisceral “metastatic” site tumor tissue in metastatic prostate cancer (mPC)

167

Background: Men with mPC with visceral metastasis, as compared to non-visceral disease have inferior outcomes regardless of therapy (PMID: 25403629). Herein, we hypothesize that visceral versus non-visceral metastasis sites differ with regards to underlying genomic alterations (GA). These GA possibly drive metastasis to visceral sites and mediate a more aggressive disease. Identifying these GA may guide future trial designs by better stratifying patients and predicting therapy responses. Methods: In this retrospective analysis, inclusion criteria were: diagnosis of mPC and comprehensive genomic profiling of metastatic tissue by CLIA certified lab. Liver and lung were defined as visceral while bone and lymph nodes were defined as non-visceral metastasis. Evaluated GA were p53, RB1, PTEN, AR, TMB, CDK12, SPOP, MYC, MET, BRCA genes, BRAF, ARID1A. Fisher’s Exact Test was used to compare GA in visceral and non-visceral tumor tissue. Results: Overall 54 men with mPC with visceral (n=8) and non-visceral (n=46) metastatic tissue biopsies were evaluated. Visceral biopsies included liver (3) and lung (5). Non-visceral biopsy sites included lymph nodes (33) and bone (13). Men with or without visceral metastasis had similar baseline characteristics (Fisher’s Exact Test and Wilcoxon Rank Test; Table). Visceral tumor tissue had a significantly greater odds of having RB1 mutation [OR = 12.09; 95% CI = (1.12, 178.21); p-value 0.02] as compared to non-visceral tumor tissue. Conclusions: RB1 GA were more common in visceral as compared to non-visceral metastatic sites in mPC. RB1 loss is associated with ineffectiveness to CDK4/6 inhibitors (PMID 26633733). These hypothesis-generating data suggest that men with mPC with visceral metastasis may not optimally benefit by enrollment on CDK4/6 inhibitor trials. BLM, NA: equal contribution.[Table: see text]

Prospective trial of nivolumab (Nivo) plus radium-223 (RA) in metastatic castration-resistant prostate cancer (mCRPC) evaluating circulating tumor DNA (ctDNA) levels as a biomarker of response

TPS267

Background: RA is a calcium-mimetic radiopharmaceutical emitter of alpha particles that has been approved for treatment of mCRPC. Radiation plus checkpoint inhibitors has demonstrated promising efficacy in previous clinical trials (PMID 27466265, 23535954). Alteration to PD-1 expression has been observed with radium-223, suggesting potential synergy with Nivo (PMID 29137877). ctDNA concentration may accurately reflect overall tumor burden and response to immune therapy. ctDNA testing after 6 weeks of therapy predicts efficacy of immunotherapy in patients with metastatic NSCLC and urothelial carcinoma (PMID 30093454) and metastatic gastric cancer (PMID 30013197). Reduction of ctDNA correlated with both radiographic progression free survival (rPFS) and overall survival. We hypothesize that RA + Nivo will be safe and decrease ctDNA, which may predict response to therapy earlier than conventional scans. Methods: This is a single-arm phase I/II investigator initiated trial (NCT04109729). Primary objectives: 1) Safety, 2) Change in ctDNA after 6 weeks treatment compared to baseline. Secondary objectives: 1) PSA-PFS; 2) PSA 50% response rate; 3) Time to skeletal related event; 4) Bone metabolism marker response. Inclusion criteria: symptomatic bone metastasis, mCRPC, adequate hematopoiesis. Exclusion criteria: visceral metastasis, history of autoimmune disease and current use of immune suppression therapy. A total of 36 patients will be enrolled. Cycles are 28 days. ctDNA concentration will be measured using GuardantOMNI research platform which evaluates 500 genes. Treatment: RA (55 kBq/kg IV) monotherapy lead in for two cycles followed by RA plus Nivo (480mg IV) for an additional 4 cycles. Nivo monotherapy then continues for up to 2 years. ctDNA collected prior to combination therapy and 6 weeks after. Restaging scans done every 2 cycles while on radium-223 and every 3 cycles while on nivolumab. Clinical trial information: NCT04109729.

A phase Ib/II trial of perioperative intratumoral MVA-BN-brachyury (MVA) plus systemic PROSTVAC and atezolizumab (Atezo) for intermediate-risk and high-risk localized prostate cancer (AtezoVax)

TPS382

Background: Many patients with intermediate or high-risk localized prostate cancer relapse after prostatectomy, identifying an unmet need. Cancer vaccines increase the infiltrating lymphocyte concentration in localized and metastatic prostate cancer (PMID 25255802, 29858218). We hypothesize that treatment with a combination of two vaccines plus PD-L1 inhibition will be safe and significantly stimulate immune infiltration within the tumor microenvironment. MVA is a modified vaccinia virus that is replication-deficient, inducing the generation of tumor antigen-specific killer T-cells. PROSTVAC is a poxviral based cancer vaccine using a vaccinia virus prime and fowlpox based boost along with co-stimulatory molecules B7.1, leukocyte function-associated antigen-3, and intercellular adhesion molecule-1. Methods: This study is a single-arm,, phase I/II investigator initiated trial (NCT04020094). Primary objectives: 1) Safety, 2) Quantitative change in infiltrating CD8+ lymphocytes between the biopsy and prostatectomy as measured by immunofluorescence. Secondary endpoints: 1) 6- and 12-month undetectable PSA rate; 2) PSA-PFS compared to institutional historic control. Inclusion criteria: unfavorable intermediate to very high-risk prostate adenocarcinoma (per NCCN). Exclusion criteria: non-adenocarcinoma histology and metastatic disease (including regional nodal metastasis). A total of 22 patients will be enrolled starting with a 6 patient safety lead in. Prostate MRI will be obtained prior to treatment. Treatment schema: 2 neoadjuvant cycles (Atezo + MVA + PROSTVAC), followed by prostatectomy then 6 additional adjuvant cycles (Atezo + PROSTVAC). Neoadjuvant cycle 1: atezolizumab (1200mg IV Q3wks), PROSTVAC-V (Prime, 2x108 Inf.U subcutaneous), MVA (2 x 108 Inf.U/0.5 ml, intra-tumoral injection, volume determined by MRI). Neoadjuvant cycle 2: atezolizumab, PROSTVAC-F (Boost, 1x109 Inf.U, subcutaneous), MVA. Adjuvant: atezolizumab and PROSTVAC-F. Clinical trial information: NCT04020094.

Response to systemic therapy and survival outcomes in de-novo (D1) metastatic castration-sensitive prostate cancer (mCSPC) versus mCSPC with prior local therapy (D0)

46

Background: A real-world study (n= 436, PMID: 29707790) suggest that D1 mCSPC has worse outcomes than D0 mCSPC. The objective of our study is to validate these findings in a real-world setting, and compare clinical and tumor genomic characteristics associated with D1 vs. D0 mCSPC. Methods: In this retrospective study, eligible patients had mCSPC, received androgen deprivation therapy (ADT) +/- intensification with docetaxel or novel hormonal therapy. D1 mCSPC was diagnosed as those with distant metastasis at the first diagnosis of prostate cancer. Progression-free survival (PFS) was per PCWG2 criteria or clinical progression, and overall survival (OS) was date of death or last follow up from start of ADT for mCSPC. Baseline clinical characteristics were compared using the t test. Survival was compared using the log-rank test with Kaplan-Meier methods. Results: Of 396 eligible patients, 242 had D1 mCSPC. Men with D1 mCSPC were younger, had significantly higher median PSA, Gleason score, and alkaline phosphatase at diagnosis of mCSPC, and had significantly shorter PFS and OS with standard ADT, as well as intensified ADT, compared to men with D0 mCSPC (Table). Conclusions: These findings validate data from a previous real-world study that D1 CSPC is associated with inferior prognosis and outcomes on systemic therapy compared to D0 mCSPC. These data may aid with counseling and treatment selection, as well as patient stratification in future trials in mCSPC. Comparison of comprehensive genomic profiling data, obtained through CLIA certified labs, will be presented at the meeting.[Table: see text]

Results from BLASST-1 (Bladder Cancer Signal Seeking Trial) of nivolumab, gemcitabine, and cisplatin in muscle invasive bladder cancer (MIBC) undergoing cystectomy

439

Background: Cisplatin-based neoadjuvant chemotherapy (NAC) in MIBC improves survival which correlates with pathologic response (PaR) at radical cystectomy (RC). The combination of immunotherapy and NAC may improve PaR and outcomes in MIBC. We tested the efficacy and safety of nivolumab (N) with gemcitabine-cisplatin (GC) as neoadjuvant therapy for MIBC in our phase II trial (NCT03294304). Methods: Eligible pts with MIBC (cT2-T4a, N≤1, M0) who were candidates for RC were enrolled. Pts received C (70mg/m2) IV on D1, G (1000mg/m2) on D1,D8 and N (360 mg) IV on D8 every 21 days for 4 cycles followed by RC within 8 weeks. The primary endpoint was PaR (≤pT1,N0). Secondary objectives were safety of GC+N and PFS at 2 years. The correlative objectives based on pre-treatment biopsies were correlation of PaR with 1) WGS 2) molecular subtypes of BC; 3) PD-L1 expression; 4) baseline TILs, CD3, CD8 and CD56.. Evaluable pts. should have received at least 1 dose of N. PaR will be summarized by the PaR rate as estimated by the sample proportion with exact 95% confidence intervals. We specified a null PaR of 0.35 and an alternative hypothesis of 0.55; we will reject the null hypothesis if at least 20 of 41 pts. have a PaR. Results: Between Feb 2018 and June 2019, 41 pts. were enrolled (cT2N0 90%, cT3N0 7%, cT4N1 3%); 2 patients refused surgery but were included in ITT population. PaR was observed in 27/41 pts. (65.8%), including pts with N1 disease. The combination was safe with manageable toxicities and no deaths from treatment. Majority of AEs were from GC; the overall rates of grade 3-4 AEs was 20%, majority being neutropenia, thrombocytopenia and renal insufficiency. Immune related AEs were seen in 3 patients, 2 had "adenitis" which wasymptomatic,1 pt developed Guillian Barre Syndrome after surgery, which resolved with IVIG; and none of them required steroids. There was no delay in time to RC and no unexpected surgical complications from treatment. Patients are being followed for progression and survival. Correlative work is ongoing. Conclusions: Neoadjuvant N+GC is safe and effective in MIBC with significant pathologic downstaging rates and no added toxicities or delay to surgery. Clinical trial information: NCT03294304.

NEXT: A phase II, open-label study of nivolumab adjuvant to chemoradiation in patients (pts) with localized muscle invasive bladder cancer

TPS605

Background: In pts with localized muscle invasive bladder cancer (MIBC), trimodality bladder preserving therapy (TMT), with transurethral resection of bladder tumor, radio-sensitizing chemotherapy and definitive radiation, has up to a 50% risk of local and systemic relapse during the 2-year post treatment phase. We hypothesize that by inhibiting immune checkpoints, chemo-radiation induced tumor specific immune response will be enhanced both locally and abscopally, resulting in better failure-free survival (FFS). In the NEXT trial, we evaluate the efficacy of nivolumab after completion of the TMT in this setting. Methods: Pts with localized MIBC who have completed standard TMT are eligible. Pts receive nivolumab 480 mg intravenously every 4 weeks for up to 12 doses. Treatment with nivolumab begins within 90 days of completion of TMT. Subjects undergo surveillance cystoscopic and scan based assessments on study. Archived tumor tissue at baseline and at relapse is obtained for correlative studies. The primary endpoint is 2-year FFS. Secondary endpoints include FFS at 2 years in patients with intact bladder, rate of radical cystectomy (RC), cystoscopic local control, distant FFS in patients with intact bladder and those that undergo RC, overall survival, toxicity and quality of life. Exploratory endpoints include to characterize changes in immune cell subsets that can be correlated with clinical outcome and to assess the correlation of response to PD-L1 expression in pretreatment tumor tissue in the study subjects. The planned sample size for this single arm, open label trial is 28 pts. Kaplan-Meier methods will be used to plot survival endpoints and cystoscopic local control rates. Exact binomial methods will be used to provide 6 months, 1-year and 2-year estimates for these endpoints. The sample size justification is based on the maximum width of a two-sided 95% binomial confidence interval for 2 year FFS. With 28 evaluable subjects, a 95% exact binomial confidence interval, estimated using the method of Clopper-Pearson, will extend no more than 20% from the observed FFS. Clinical trial information: NCT03171025.

Randomized phase II trial of radium-223 (RA) plus enzalutamide (EZ) versus EZ alone in metastatic castration-refractory prostate cancer (mCRPC): Long-term follow up of secondary endpoints

125

Background: RA, a bone targeting alpha radiopharmaceutical, and EZ, are approved for mCRPC. Per phase 3 SWOG0421 trial, men with mCRPC and a significant decline in serum bone metabolism markers (BMM) had improved survival with atrasentan, a bone targeting agent (PMID 24565955). We hypothesized that RA+EZ is safe, and decrease bone metabolism markers compared to EZ alone. Here we report the long-term follow up of the secondary clinical endpoints. Methods: In this phase 2 trial (NCT02199197), men with progressive mCRPC were treated with EZ (160 mg daily) ± RA (standard dose of 55 kBq/kg IV Q4 weeks x 6), until disease progression or unacceptable toxicities. Primary objectives: 1) changes in N-telopeptide compared from baseline to end of treatment; 2) safety. Secondary objectives: changes in 4 other markers of bone resorption or formation, and PSA progression free survival (PSA-PFS), radiographic PFS (rPFS) and overall survival (OS). Results: After a safety lead in phase (n=8), 39 men were randomized (2:1) to RA+EZ vs EZ. Median follow up is 19.3 months (range 3 – 24 months). Combining RA+EZ was safe (2018 ASCO annual meeting abstract: 5057) and met the primary endpoint (2018 ESMO annual meeting: Annals of Oncology). There was a consistent trend regarding PSA-PFS, rPFS and OS favoring RA+EZ over EZ. . . (Table). Notably, no bone fractures have occurred in either group with extended follow up. Conclusions: The use of RA+EZ was safe with a longer follow up with no increase in skeletal related events including fractures. All secondary endpoints, numerically favored RA+EZ vs EZ. Clinical trial information: NCT02614859.

Association of serum iron and response to immune checkpoint inhibitors (ICIs) in metastatic clear cell renal cell carcinoma (mccRCC)

723

Background: ICIs have improved survival in mRCC patients (pts), yet response rates (RR) to these treatments are variable. Biomarkers predictive of response to ICIs may improve outcomes for mccRCC pts. Genes that promote tumor-specific iron accumulation such as hepcidin (HAMP) or transferrin (TF) are significantly correlated with decreased overall survival in clear cell RCC (TCGA-KIRC). Iron deficiency in cancer patients is positively correlated with tumor stage and inversely proportional to treatment response (PMID: 23567147). Here, we investigate whether serum iron profile may be associated with response to ICIs in mccRCC pts. Methods: Clinical data was obtained from an mRCC registry at the Huntsman Cancer Institute, University of Utah. Analyses were limited to mccRCC pts who had serum iron studies within 6 months before initiating an ICI and had been assessed for RR. ICIs included nivolumab + ipilimumab, atezolizumab, or nivolumab alone. Responses were defined as complete response (CR), partial response (PR), stable disease (SD), or progressive disease (PD) by RECIST criteria. Clinical benefit (CB) was defined as CR + PR + SD. Descriptive statistics were used to assess associations between iron stores and response to ICIs and IMDC criteria. Results: 36 pts met all aforementioned eligibility criteria (29 were of IMDC intermediate risk, 7 were of IMDC poor risk). 5 pts received a first-line ICI, and the remaining 31 pts received ICIs as salvage therapy. Pts with CB had a significantly higher median serum iron level compared to those with no CB (59 vs 38.5 ug/dL; p=0.024). Furthermore, pts with normal transferrin saturation (TSAT %) were more likely to derive CB from ICIs (p=0.048). No association was found between serum ferritin (a marker of inflammation and tissue iron) and response to ICIs. Conclusions: In this hypothesis-generating study, increased serum iron, and TSAT levels within the normal range are associated with an increased likelihood of response to ICIs in pts with mccRCC. Once validated, these results may establish serum iron profile as a predictive marker of response to ICIs, in addition to providing the rationale for ruling out iron deficiency before starting ICIs.

Identification of genomic alterations in signaling pathways associated with poor survival in newly diagnosed metastatic prostate cancer (mCSPC) using artificial intelligence (AI)

169

Background: Although the survival outcomes for patients with mCSPC has improved over the last 5 years, disease remains universally fatal even with improved therapies. Currently, genomic information from the tumor is not taken into account for treatment selection and prognostication. AI is increasingly being used in clinical cancer genomics research. Probabilistic Graphical Models (PGMs) are AI algorithms that capture multivariate, multi-level dependencies in complex patterns in large datasets while retaining human interpretability. We hypothesize that PGMs can establish correlation of baseline somatic genomic alteration with poor survival outcomes in mCSPC. Methods: Eligible men had new mCSPC starting systemic therapy and had tumor genomic profiling done through a CLIA certified lab. Gene alterations with known pathogenicity were grouped into canonical pathways. Multilevel associations between survival, clinical variables (including baseline PSA, Gleason ≥ 8, and visceral metastasis), and genomic signatures (PI3K/AKT/mTOR, HRR, G1/S Cell Cycle, SPOP, TP53, WNT, and MYC) were assessed using a Bayesian Network (BN), and confidence intervals were estimated by bootstrapping. A Kaplan-Meier (KM) survival analysis was performed independently to support the results generated by the BN. Results: Among all variables, only genomic alterations in TP53 and the G1/S pathway were significantly associated with poor overall survival by BN analysis. KM analysis showed concordant results for TP53 (median OS, altered 50 mos vswild-type 84 mos; HR=2.79, 95% CI 1.63 – 4.80; P=0.0002) and G1/S (median OS altered 23 mos vswild-type 73 mos; HR=8.21, 95% CI 3.40 – 19.86; P<0.0001). Conclusions: These hypothesis-generating data reveal genomic signatures associated with poor survival in mCSPC patients. Our results, after external validation, may aid with counseling and treatment selection, as well as patient stratification in future trials in mCSPC.

Identification of genomic aberrations associated with overall survival in metastatic clear cell renal cell carcinoma (mccRCC)

745

Background: Tumor comprehensive genomic profiling (CGP) in addition to risk stratification by IMDC criteria may aid in improving risk stratification. The objective of this study was to assess the prognostic impact of somatic mutations in addition to IMDC risk criteria. Methods: All patients with mccRCC treated with first line with VEGFR-TKI with CGP data available through a CLIA certified lab were included. Kaplan-Meier methodology and Cox proportional hazard ratios were used to test the association of overall survival with genomic alterations present in at least 7% of the population in this dataset. Genomic data were correlated with outcome by univariate analysis and subsequent multivariate testing, integrating genomic data with IMDC risk criteria. Results: A total of 58 patients met eligibly. The presence of any mutation in VHL, PBRM1, and MLL2 were prognostic in terms of overall survival (Table). The mutation status for these three prognostic genes was added to the IMDC risk model to test for the prognostic correlation. The mutations status of these 3 genes significantly correlated with overall survival (VHL: 0.32 [95% CI 0.11-0.95], PBRM1: 0.36 [0.14-0.96], and MLL2: 7.60 [1.35-24.6]) independent of the IMDC risk criteria. Conclusions: In mccRCC, VHL, PBRM1, and MLL2 mutations each predict overall survival independent of IMDC criteria. Further studies are warranted to assess alterations with low prevalence in this data set. Upon external validation, these data provide the rationale for integration of mutation status of these three genes in to the IMDC risk criteria.[Table: see text]

Impact of somatic SPOP (Speckle-Type POZ protein) mutation (mtSPOP) on response to systemic therapy and survival outcome in men with de novo metastatic castration-sensitive prostate cancer (d-mCSPC)

329

Background: Men with metastatic castration resistant prostate cancer harboring somatic mutant SPOP (mt SPOP) have improved progression free survival (PFS) on abiraterone than those with wild-type SPOP (wt SPOP) (Boysen et al, CCR 2018; PMID: 30068710). We hypothesized that mtSPOP will be associated with improved response to systemic therapy and outcomes in mCSPC. Methods: This retrospective study included patients from 4 academic institutions. Eligibility criteria: receipt of standard androgen deprivation therapy (ADT) without intensification (chemotherapy or novel hormonal agents) for the diagnosis of d-mCSPC, no prior history or treatment for prostate cancer, and established SPOP status determined by targeted next-generation sequencing. PFS was defined per PCWG2 defined PSA or investigator assessed radiographic progression. Overall survival (OS) was calculated from date of starting ADT for d-mCSPC to date of death. Kaplan-Meier analysis and t-test were used to compare variables in these two cohorts. Results: Of 110 mtSPOP men with advanced prostate cancer identified, 37 had d-mCSPC of which 25 received ADT. Of 353 wtSPOP patients, 184 had d-mCSPC of which 97 received ADT. Baseline demographics and disease characteristic were similar (table). mtSPOP was associated with significantly improved PFS [35 vs. 14 months, HR 0.519 (95% CI 0.312-0.861), p=0.011] and OS [97 vs. 69 months, HR 0.4392 (95% CI=0.207-0.931); p=0.032] with ADT as compared to wtSPOP patients. Conclusions: Men with d-mCSPC with somatic mtSPOP have improved outcomes with ADT than those with wtSPOP. Once validated, these hypothesis generating data may aid with counselling and treatment selection, as well as patient stratification in future trials in d-mCSPC.[Table: see text]

Genomic correlates of response to PD-1 axis inhibitors (IO) in metastatic urothelial cancer (mUC) using explainable artificial intelligence (AI)

570

Background: AI is increasingly being used in clinical cancer genomics research. Probabilistic Graphical Models (PGMs) are AI algorithms that capture multivariate, mutli-level dependencies in complex patterns in large datasets while retaining human interpretability. We hypothesize that PGMs can identify clinical and genomic features that correlate with IO response in patients (pts) with mUC. Methods: In this retrospective study eligibility criteria were: diagnosis of mUC, receipt of IO for mUC, comprehensive genomic profiling data available from CLIA certified labs. The Bayesian Network (BN, PGM based AI) was used to discover clinical characteristics and selected genomic alterations relevant to IO response by RECIST 1.1 (investigator assessed). Results: Overall, 95 pts (73 men) with mUC were evaluated. 45 (47%) were ever smokers.The presented BN correctly captured the clinical landscape of mUC explaining significant relationship between included variables (p<0.0001). Ever smokers and pts with de novo metastasis had higher TMB and better response to IO. Inactivating MLL2 alterations were more prevalent in non-smokers, and negatively correlated with response to IO. FGFR3 alterations did not predict response to IO. Significant associations are presented in Table. Conclusions: These hypothesis-generating data (by a novel approach, i.e. PGM based AI) showed that smoking and high-TMB were associated with improved response to IO; in contrast, inactivating MLL2 alternations and visceral metastasis predicted inferior response. FGFR3 alterations did not correlate with response. This model validated previous findings and found new hypothesis-generating relationship, such as altered MLL2 gene; external validation is needed.[Table: see text]

Genomic landscape of metastatic hormone sensitive prostate cancer (mHSPC) vs. metastatic castration-refractory prostate cancer (mCRPC) by circulating tumor DNA (ctDNA)

5043

Background: mCRPC carries a poor prognosis, and targeted therapies have had minimal success in mCRPC. Novel genomic targets could improve drug development. To date, large ctDNA studies in metastatic prostate cancer have been descriptive with limited or no clinical annotation. Herein, we hypothesize that profiles of genomic alterations (GAs) in ctDNA not only differ significantly between, but can also be used to predict mCRPC vs. mHSPC. These findings could help identify new drug targets for mCRPC treatment. Methods: Men with mHSPC or mCRPC who underwent NGS of ctDNA using G360 (Guardant Health Inc.) at the Huntsman Cancer Institute were included. Men were classified as mCRPC or mHSPC (patients with current or no prior ADT). G360 detects somatic mutations in selected exons of 73 genes, amplifications in 18 genes, and selected fusions in 6 genes. Two-sided students t-test was used to compare the %cfDNA and total GAs. The Chi squared test was used to compare the frequency of each GA. Machine learning (ML) algorithms were trained on GAs and benchmarked by cross-validated performance. GAs contributing to mCRPC vs. mHSPC classification were measured by ML feature importance (e.g. odds ratios, regression coefficients). Results: Of the 259 men included, 119 men had mHSPC and 140 had mCRPC. Men with mCRPC had more GAs (4.5 vs. 1.86, p<0.0001) and higher %cfDNA (9.56% vs. 5.02%, p=0.02). In mHSPC, there was no significant difference in the number of GAs or %cfDNA between men on ADT and those who hadn’t yet started ADT. ML algorithms used GAs to predict mCRPC with 78.1% sensitivity, 64.0% specificity, 76.7% PPV, 65.1% NPV, and 70.3% overall accuracy. mCRPC was enriched with GAs in AR, ARID1A, BRAF, BRCA2, CCNE1, CTNNB1, EGFR, FGFR1, KIT, MET, MYC, PDGFRB, PIK3CA, and TP53. Of note, many of these genes are involved in MAP/ERK signaling. Conclusions: Men with mCRPC have more GAs, higher %cfDNA, and enrichment of GAs in the MAP/ERK pathway compared to men with mHSPC. The distinct GAs seen in mCRPC represent novel therapeutic targets, especially in the MAP/ERK pathway. We also show that machine learning can differentiate mHSPC and mCRPC based on GAs detected in ctDNA.

PrE0807 phase Ib feasibility trial of neoadjuvant nivolumab (N)/lirilumab (L) in cisplatin-ineligible muscle-invasive bladder cancer (BC)

TPS4594

Background: Neoadjuvant cisplatin-based chemotherapy before radical cystectomy (RC) improves outcomes but ~50% of patients (pts) are cisplatin-unfit. Anti-PD(L)1 agents can prolong overall survival (OS) in platinum-resistant advanced BC and have shown high pathologic complete response rate (pCR) and safety as single agent in phase II trials in the neoadjuvant setting. The combination of anti-PD-1 and anti-KIR agents is feasible and very attractive based on complementary and non-overlapping roles in regulating adaptive and innate immune response as well as impacting the function CD8+ T and NK-cells. Higher CD8+ T cell density (TCD) at RC tissue correlates with longer OS. We hypothesize, that combining anti-PD1 (N) with anti-KIR (L) is safe and feasible as neoadjuvant therapy in cisplatin-unfit pts and results in high CD8+ TCD at RC. Methods: Phase Ib multi-institutional trial evaluating 2 doses (4 weeks apart) of N alone or N+L in 2 cohorts; pts will be assigned sequentially to N (Cohort 1), and if there is no negative safety signal after the first 12 pts, subsequent pts will be assigned to N+L (Cohort 2). Key eligibility: cT2-4aN0-1M0 stage, ≥20% tumor at TURBT, adequate organ function, no autoimmune disease within 2 years, no concurrent invasive upper urinary tract carcinoma or other active cancer. Primary endpoint: safety based on CTCAE v5.0 measured as the rate of ≥G3 treatment related adverse events (AE). Key secondary endpoints: CD8+ TCD absolute and % change between TURBT and RC, % of pts who do not get RC within 6 weeks after neoadjuvant treatment due to treatment-related AE, % pCR, recurrence-free survival, and evaluation of biomarkers in tumor tissue, blood, urine. Rates of ≥Grade 3 AE with neoadjuvant treatment will be reported along with 90% exact binomial CI. In Cohort 1, maximum CI width is 0.51; in Cohort 2, it is 0.36. Our hypothesis is that the change in CD8+ TCD between TURBT and RC will be about 3 CD8+ T cells / 100 tumor cells within HPF. Up to 43 pts will be enrolled for 36 eligible, treated pts (12:N, 24:N+L). Cohort 1 and 2 have 81% and 98% power, respectively, to detect the hypothesized difference with 1-sided type I error rate of 0.05. Trial is open to accrual in US. Clinical trial information: NCT03532451.

Efficacy of alpha-1,3-galactosyltransferase-expressing allogeneic renal cell carcinoma immunotherapy in patients (pts) with refractory metastatic renal cell carcinoma (mRCC)

590

Background: HyperAcute Renal (HAR) immunotherapy consists of two allogeneic renal cancer cell lines that have been genetically modified to express α(1,3)Gal, to which humans have an inherent pre-existing immunity. A previous report demonstrated that HAR is well tolerated in pts with mRCC (2017 GUASCO, abstract: 528). Herein, we report the efficacy of HAR immunotherapy in mRCC. Methods: Pts with refractory clear-cell mRCC were eligible for this phase 1 dose-escalation trial. Concomitant treatment (Rx) with other approved agents was permitted after initial 2 months (m) of HAR monotherapy. The trial followed a standard 3+3 design with cells injected intradermally weekly for 4 weeks then biweekly injections for 10 immunizations (150 x106cells then escalated to 300 x106cells). Co-primary objectives were safety and efficacy. Results: A total of 18 patients were enrolled (4 low dose, 14 high dose) between 06/2015 to 07/2016. Patients received a median of 1 systemic Rx prior to HAR immunotherapy, with 8 patients receiving 2 or more prior agents. IMDC risk categories at the time of initial metastatic disease were: favorable risk (33%), intermediate risk (66%), poor risk (0%). The ORR was 0% with a disease control rate of 50%. Median PFS for patients treated with HAR immunotherapy was 2.0 months (m) (range 1.7-30.3 m). For patients receiving the low dose HAR, median overall survival (OS) was 14.2 m (range 3.6-21.6 m), while median OS for high dose HAR was 25.3 m (5.8-29.3 m). At the time of data cutoff in 09/2018, 7 patients were still living. Detailed clinical data will be presented in the meeting. Conclusions: HAR immunotherapy in refractory mRCC was well tolerated and demonstrated potential efficacy for OS similar to currently approved salvage-line Rx. With a unique mechanism of action, HAR immunotherapy may be a candidate for inclusion in novel combinatorial regimens being developed in salvage therapy setting in pts with mRCC. Clinical trial information: NCT02035358.

Validation of plasma miR-371a-3p expression in patients with metastatic and early stage germ cell tumor

526

Background: Identification of relapsing/residual viable germ cell malignancy (GCM) is often challenging in patients with CSI on surveillance or with residual post-chemotherapy disease. The presence of a biomarker for GCM would overcome the uncertainty of the current methods and improve the quality of care of those patients. Methods: A 2-cohorts pilot study involving patients with clearcut evidence of GCM (clinical stage IS, metastatic and GCM prior orchiectomy) for the development cohort and patients with CSI with or without signs of tumor relapse and patients with metastatic GCM post-chemotherapy for the validation cohort. Blood samples collected in Streck tubes were obtained prior to chemotherapy for the development cohort and post-orchiectomy, at the time of suspicious relapse or post-chemotherapy in the validation cohort. Plasma miR-371a-3p (miR371) was analyzed by RT-PCR. Positive predictive value (PPV), sensitivity, specificity, negative predictive values (NPV) and AUC of the ROC for miR371 and standard diagnostic tools (CT scan, AFP, BHCG and LDH) were calculated correlating qualitative miR371 expression to the presence of viable GCM. Results: 132 patients were enrolled into the development (33 pts) and validation (99 pts) cohorts. Within the development cohort 31/33 pts were miR371 positive, 2/33 pts were negative. 31 true positives were found among the 31 miR371 positive patients for a PPV of 100% (31/31). Two true negatives were found among the 2 patients who had no miR371 expression identified (teratoma, lymphoma). The validation cohort was chosen to evaluate the methodology among patients with predicted lower volumes or no clinically apparent disease. 13/99 patients within the validation cohort were miR371 positive and all 13 had subsequent confirmation of viable GCM. For the overall study of 132 pts, PPV was 100% (46/46), NPV 98%, sensitivity 96% and specificity 100%, the AUC of the ROC was 0.96. Conclusions: Detectable circulating miR-371a-3p levels predict viable GCM and may represent a strategy for biological rather than radiographic assessment for surveillance of early stage and for post-treatment patients. Larger studies to validate these and like results have been planned.

A phase II, multicenter, single-arm trial of CV301 plus atezolizumab (Atezo) in locally advanced (unresectable) or metastatic urothelial cancer (UC)

TPS494

Background: Anti-PD1/PD-L1 can achieve durable responses in advanced UC but most patients (pts) do not respond. Combination strategies with agents that “prime” the immune system may improve outcomes. CV301 comprises two recombinant poxviruses, Modified Vaccinia Ankara (MVA) and Fowlpox (FPV), encoding the human transgenes for CEA, MUC-1, and a Triad of Co-stimulatory Molecules (TRICOM: ICAM-1, LFA-3, and B7-1). MVA-CV301 is used for priming doses and FPV-CV301 is used for booster doses to achieve a heterologous prime boost regimen. In preclinical studies, BN-platform vaccine plus PD1/PD-L1 inhibitors exhibited synergistic anti-tumor efficacy, T-cell infiltration, and PD-L1 upregulation in tumors. CEA and MUC-1 are expressed, in 41-90% and 55-91% of any stage UC, respectively, and in ~100% of metastatic UC. An ongoing Phase Ib trial of CV301 plus anti-PD-1 agent has demonstrated a similar safety profile to anti-PD-1 monotherapy with only mild vaccine-related adverse events (AEs). Methods: This is a Phase 2, single-arm, multi-institutional trial designed to study CV301 plus atezo as 1st-line treatment in pts with advanced UC ineligible for cisplatin-based chemotherapy regardless of PD-L1 (Cohort 1) and as salvage treatment in pts with UC progressing after platinum-based chemotherapy (Cohort 2). MVA-CV301 is given subcutaneously (SC) on Days 1 and 22 and FPV-CV301 SC every 21 days for 4 doses, then every 6 weeks until 6 months, then every 12 weeks until 2 years. Atezo 1200mg is given every 21 days. Primary endpoint is objective response rate (ORR; RECIST 1.1). Secondary endpoints: immune response, OS, PFS, response duration, AEs. Tumor and serial blood samples will be collected for biomarker analyses; 1-sided α is 0.025/cohort in this design. With a 2-stage design, success criteria are based on historic ORR (H0) and alternative ORR (H1) with ≥70% power. For Cohort 1, assuming H0 = 0.23, H1 = 0.43, then Cohort 1 sample size N1= 14, responders required at stage 1 to continue R1≥3, total accrual goal N = 33, total responders to reject H0, R≥13. For Cohort 2, assuming H0 = 0.15, H1 = 0.33, then N1= 13, R1≥2, N = 35, R≥10. Accrual has begun; completion is expected within 1 year. Clinical trial information: NCT03628716.

Risk factors for venous thromboembolism (VTE) during chemotherapy in patients with germ cell tumors (GCT)

520

Background: The Khorana score is the primary tool utilized to predict VTE risk in patients with cancer. This score incorporates primary cancer site, pretreatment hematologic parameters, and body mass index. GCT are considered high-risk for VTE. However, risk factors for VTE not included in the Khorana Score have been reported for GCT including retroperitoneal lymph node (RPLN) size, elevated LDH, and poor risk disease. Methods: A retrospective chart review was conducted to correlate known VTE risk factors with VTE incidence in male patients with GCT undergoing first-line chemotherapy. Variables included venous access type, RPLN size, LDH, chemotherapy regimen, procedure history, cancer stage and histology, Khorana risk factors, and pertinent demographics. VTE and superficial vein thrombosis (SVT) events that occurred within 1 month prior through 6 months after start of chemotherapy were recorded. Fisher’s Exact test was used for univariate analysis and logistic regression for multivariate analysis of the relationship between predictors and thrombosis. P-values are two-sided at an alpha level of 0.05. Results: 47 patients with GCT were identified. 12 VTE occurred (overall incidence 25.5%), 11 in patients with central lines (39.3% incidence) and 1 with a peripheral line (5.3% incidence). SVT were observed in 5 patients with peripheral lines compared to 1 patient with a central line (26.3% vs. 3.6%). Central line access was the primary variable associated with VTE risk in both univariate and multivariate analysis (p=0.01 and p=0.03, respectively). Conclusions: Venous access type is a significant but modifiable factor that can be targeted to reduce VTE risk. Due to small sample size there is limited statistical power to detect potentially meaningful differences in known risk factors. If validated, these results may identify specific patients to be treated with prophylactic anticoagulation. [Table: see text]

Receipt of systemic therapy in older versus younger patients (pts) with metastatic renal cell carcinoma (mRCC)

580

Background: More than half of pts diagnosed with mRCC are age 65 or older. However, older pts are often under-accrued/under-represented in clinical trials, partly due to concerns about their ability to tolerate systemic therapy (Rx). Given this, efficacy data from the registration trials may not apply to older pts. Herein, we investigate whether older patients with mRCC are less likely to receive various lines of systemic Rx than their younger counterparts. Methods: Clinical data was obtained from a prospectively maintained mRCC registry at the Huntsman Cancer Institute, University of Utah. Older pts were defined as ≥65 yrs at initiation of first-line systemic Rx for mRCC. Univariate analyses of the lines of systemic Rx received were performed using the Chi-squared test. Comparison of ordered categorical variables was made with the Wilcoxon rank sum test. Results: 264 pts who received first-line Rx for mRCC between 2004-2018 were included, and 108 of them were older pts. For older pts, median age at first-line Rx was 71.1 years and 78.7% had clear cell histology, whereas, the median age for younger pts was 53.4 years and 75.6% had clear cell histology. There was no difference in the baseline IMDC risk categories in older vs. younger pts (p = 0.907). A similar proportion of older and younger pts received at least two lines of systemic Rx (66.9% vs. 62.4%, p = 0.532). Furthermore, when analyzed across all lines of treatment, there was no difference in the number of systemic Rx between older and younger pts (p = 0.593). The median OS was similar in both groups: older 30 months (95% CI 21-44 months) vs. younger 34 months (95% CI 30-46 months) (p = 0.639). Conclusions: Older pts with mRCC receive a similar number of systemic Rx as their younger counterparts, and have similar survival outcomes. These findings can inform clinicians when selecting first and salvage-line treatment for older pts, and warrant proportionate accrual and representation of older pts in clinical trials.

Germline variant in SLCO2B1 and response to abiraterone acetate plus prednisone (AA) in men with metastatic castration-resistant prostate cancer (mCRPC)

311

Background: Currently, there are no predictive biomarkers of response to AA in mCRPC routinely used in the clinic. SLCO2B1 encodes a sodium-independent organic anion transporter that mediates transport of endogenous sex hormones and drugs, including AA, into tissue. Single nucleotide polymorphisms (SNPs) in SLCO2B1 are a validated predictive biomarker of response to androgen deprivation therapy in hormone sensitive prostate cancer. In a recent pre-clinical study, the AA/AG genotype for rs12422149 and the AA genotype for rs1789693 of SLCO2B1 had significantly higher mean tissue abiraterone levels. We hypothesize that the variant allele for rs12422149 and rs1789693 are predictive of improved response to AA in mCRPC. Methods: Clinical data and samples were analyzed from a prospective prostate cancer registry at the University of Utah (Salt Lake City, UT). Genotyping was performed using the Illumina OmniExpress genotyping platform. Primary endpoint was progression-free survival (PFS) on first-line AA in men with mCRPC. We performed pre-specified multivariate Cox regression analyses to assess the independent predictive value of SLCO2B1 rs12422149 and rs1789693 on PFS on AA (table). Results: 76 men with mCRPC treated with first-line AA were included. In a multivariate analysis for rs12422149, a trend towards improved median PFS was seen with the AG genotype (11.2 months) vs. the GG genotype (6.4 months) (HR 0.50, 95% CI 0.24-1.02, p=0.056). No such correlation was seen with rs1789693 genotypes. Conclusions: Consistent with pre-clinical studies, the AG genotype in rs12422149 of SLCO2B1 may be predictive of response to AA in men with mCRPC. This hypothesis-generating data needs further interrogation in larger and independent cohorts. [Table: see text]

Independent assessment of TP53 and PTEN as predictors of response to enzalutamide (ENZ) or abiraterone acetate (AA) in men with metastatic castration-resistant prostate cancer (mCRPC)

351

Background: Alterations in androgen receptor signaling are well-established mechanisms of resistance to medical castration. Pre-clinical studies suggest that alterations to key tumor suppressor genes, such as TP53 or PTEN, may also be associated with development of androgen independence as an alternate mechanism of castration-resistance. Previous studies have shown that TP53 inactivation and PTEN loss are predictive of response to novel androgen axis inhibitors. Here, we independently assess whether TP53 and PTEN genomic alterations are predictive of response to ENZ and AA in men with mCRPC. Methods: Clinical data and samples were analyzed from a prospective prostate cancer registry at the University of Utah (Salt Lake City, UT). Next-generation sequencing (NGS) was performed on predominantly primary tumor tissue for 343 somatic and germline genetic alterations using FoundationOne. Primary endpoints were progression-free survival (PFS) and overall survival (OS). Patients with mCRPC who were treated with any line AA or enzalutamide were included. We performed a univariate analysis to assess the predictive value of TP53 and PTEN. Only patients treated with single-agent therapy were included. Results: Of 141 men with prostate cancer and NGS available, 56 were included. Most patients were treated with abiraterone (n = 50), and only 6 with enzalutamide. 28.6% had PTEN loss and 35.7% had a TP53 mutation. OS and PFS did not differ significantly according to PTEN or TP53 status. Median OS was 40.9 months and not reached for men with and without TP53 mutation (HR 1.85, p = 0.31). Median PFS was 7.5 months and 9.5 months for men with and without TP53 mutation (HR 1.18, p = 0.60). Median PFS was 7.2 months and 9.5 months for men with and without PTEN loss (HR 1.15, p = 0.66). Median OS for PTEN was not mature enough to analyze. Conclusions: In our independent cohort, neither TP53 mutation nor PTEN loss is predictive of response to androgen-directed therapy in men with mCRPC patients. However, this is a relatively small retrospective sample with few events. These results should be considered exploratory only.

P53 status in primary tumor predicts efficacy of first-line abiraterone and enzalutamide in castration-resistant prostate cancer patients

5064

Background: We tested whether tissue-based analysis of p53 and PTEN genomic status, measured predominantly in primary tumor samples, may be predictive for sensitivity to abiraterone and enzalutamide in castration resistant prostate cancer (CRPC). Methods: We performed a retrospective analysis of 309 consecutive patients with CRPC treated with first-line abiraterone or enzalutamide. Of these, 116 men (38%) had available tumor tissue for analysis, and formed the basis of this study. Deleterious TP53 missense mutations and PTEN deletions were interrogated using genetically validated immunohistochemical assays for p53 protein nuclear accumulation and PTEN protein loss. OS and PFS were compared between patients with and without p53 and/or PTEN alterations. Results: 46% of evaluable cases had PTEN loss and 27% had p53 nuclear accumulation. 45% (53/118) of cases underwent targeted next generation sequencing and p53 nuclear accumulation was 91% sensitive and 90% specific for underlying TP53 missense mutation. OS and PFS did not differ significantly according to PTEN status but were associated with p53 status. Median OS was 15.8 months (95% CI, 15.8–23.9) and 28.7 months (95% CI, 28.7–42.7) for men with and without p53 nuclear accumulation, respectively (HR 1.98; P = 0.007). Median PFS was 5.5 months (95% CI, 3.53–10.5 months) and 10.2 months (95% CI, 7.37–13.3 months) in men with and without p53 nuclear accumulation, respectively (HR 1.73; P = 0.013). In multivariable analyses, p53 status was independently associated with both OS (HR 2.13; P = 0.016) and PFS (HR 1.83; P = 0.034). This effect was also seen in the subset of patients with prostatectomy tissue only. In patients with p53 nuclear accumulation median PFS (p < 0.001) and median OS (p < 0.001) were decreased compared to wild-type patients. No effect was seen with PTEN loss in either PFS (p = 0.12) or OS (p = 0.50). Conclusions: p53 status may be a biomarker of sensitivity to novel hormonal therapies in CRPC. PTEN was not a biomarker of sensitivity in our study. These results require prospective validation.

Exploring optimal sequence of abiraterone and enzalutamide in patients with castration-resistant prostate cancer: The Kyoto-Baltimore collaboration

219

Background: Abiraterone (ABI) and enzalutamide (ENZA) are novel hormonal treatments for castration-resistant prostate cancer (CRPC) used before and after docetaxel (DTX) chemotherapy. We aimed to evaluate and compare the efficacy of sequential treatment with ABI followed by ENZA or vice versa in patients with CRPC, using combined data from two institutions. Methods: We retrospectively evaluated data on 352 consecutive patients who had received both ABI and ENZA for CRPC at Kyoto University Hospital and at Johns Hopkins Sidney Kimmel Comprehensive Cancer Center. Using Kaplan-Meier analysis and log-rank tests, we compared PSA progression-free survival (PSA-PFS) and overall survival (OS) in patients treated with sequential ABI-to-ENZA versus ENZA-to-ABI without intervening therapies. Results: The number of patients receiving ABI-to-ENZA and ENZA-to-ABI were 163 (pre-DTX: 116, post-DTX: 47) and 189 (pre-DTX: 85, post-DTX: 104), respectively. The > 50% PSA response rates to ABI and ENZA were 47% and 52% in the first-line CRPC setting, and were 9% and 29% in the second-line setting. In the pre-DTX population, median PSA-PFS was not significantly different between ABI (median: 194 days) and ENZA (median: 126 days) in the first-line setting (p = 0.411), but there was an advantage favoring ENZA (median: 91 days) compared to ABI (median: 55 days) in the second-line setting (p = 0.008). Furthermore, the combined PSA-PFS was significantly longer in the ABI-to-ENZA sequence (median: 455 days) than in the ENZA-to-ABI sequence (median: 296 days) (p < 0.001). There was no statistical difference in OS between the two sequences (p = 0.598). Conclusions: The ABI-to-ENZA sequence may have more favorable efficacy in terms of combined PSA-PFS than the ENZA-to-ABI sequence, although no differences in OS were observed. This may possibly be attributable to higher PSA response rates and longer PSA-PFS to second-line ENZA compared to ABI (i.e., ENZA retains activity after ABI but not vice versa).

Incidence and characterization of antiandrogen withdrawal syndrome (AAWS) after enzalutamide (ENZA) in patients (pts) with metastatic castration-refractory prostate cancer (mCRPC)

228

Background: AAWS manifested as PSA decline after discontinuation of first generation AAs, like bicalutamide, has been well characterized and reported. Objective of this study was to assess the incidence and characterize AAWS after ENZA in pts with mCRPC. Methods: From a single institution cohort, pts with mCRPC who discontinued ENZA after documented disease progression per PCWG2 criteria were included. AAWS after ENZA was defined as any degree of PSA decline after discontinuation of ENZA. Baseline pts, disease, and treatment characteristics were compared between Òpts with AAWS after ENZAÓ vs. Òpts without AAWS after ENZAÓ treated during the similar time period: median values were compared with the Wilcoxon rank sum test; proportions were compared with FisherÕs Exact test; and the log rank test was used to compare PFS (Table). Results: 5 pts of 72 eligible pts (~7%) experienced AAWS after discontinuation of ENZA. The levels of PSA decline were as follows: 84%, 32%, 17%, 15% and 15%, respectively. Median AAWS response time, until subsequent PSA progression, was 6 weeks. None of the pts, disease or treatment characteristics (such as prior duration of response to ENZA) were different among Òpts with AAWS after ENZAÓ vs. Òpts without AAWS after ENZAÓ. Conclusions: This is the largest study reporting on the incidence and characterization of AAWS after ENZA. AAWS after ENZA is infrequent (~7%), of short duration (6 weeks), and not predicted by pts, disease or treatment related characteristics. Unlike AAWS after first generation AR inhibitors, like bicalutamide, the AAWS after ENZA is not clinically meaningful and should not have any bearing on the eligibility criteria of clinical trials conducted in the post ENZA setting. [Table: see text]

Genomic diversity between primary tumor tissue and tumor circulating cell-free DNA (cfDNA) in patients (pts) with metastatic prostate cancer

189

Background: Tumor tissue and tumor cfDNA next-generation sequencing (NGS) tests are obtained in pts with metastatic prostate cancer and have demonstrated a diverse genomic landscape. High-level evidence does not exist for utilizing these tests to guide treatment selection in these pts. Targeted therapies are available for metastatic prostate cancer treatment and clinical trials are investigating drugs targeting specific molecular pathways. The objective of this study was to assess type and number of genomic aberrations between tumor tissue and cfDNA. Methods: Pts with metastatic prostate cancer who had both tissue and cfDNA results were selected and genomic profiles were compared between these two technologies. The mean number of tissue mutations was compared to cfDNA mutations for all pts using the t-test. The mutations for both tests were then categorized into five pathways: DNA repair, cell cycle regulation, PI3K, epigenetics, and androgen receptor (AR). For each pathway, the total number of patients with a mutation was compared between tissue and cfDNA using the Mann-Whitney test. Results: Nineteen pts were identified with both tissue and cfDNA results. The mean number of mutations identified was significantly less with cfDNA (95% CI, 2.7-5.3) compared to tissue (95% CI, 7.0-9.7; P < 0.0001). There were significantly more patients with PI3K pathway mutations identified in the tissue compared to cfDNA (73.7% vs 21.1% P = 0.0018), as well as epigenetic mutations (47.4% vs 0.0% P = 0.0012). There was no difference in the number of patients identified to have DNA repair, cell cycle regulation, and AR variances between the two tests. Conclusions: The lower number of aberrations detected by the cfDNA test may have occurred due to lower sensitivity of cfDNA compared to tissue based NGS. Discordance in the type of genomic variances between the two tests suggests intra-individual genetic diversity, and these results may have implications in treatment selection of pts with metastatic prostate cancer. Data are hypothesis generating and need further investigation in a larger cohort.

Intra-individual genomic diversity between circulating tumor cell-free DNA (cfDNA) and tumor tissue testing in metastatic renal cell carcinoma (mRCC)

444

Background: Multiple approved targeted therapies are available for treatment of mRCC. Though some clinical trials guide treatment selection, there are many gaps without high-level evidence. Both tumor tissue and cfDNA based next-generation sequencing (NGS) testing are frequently performed to help guide treatment. Our objective was to assess type and number of genomic aberrations among tumor tissue and cfDNA. Methods: 14 sequential pts with both tissue and cfDNA NGS testing were selected and genomic profiles were compared. The total number of aberrations detected was statistically evaluated using comparison of the means. The Mann-Whitney test was used to compare the incidence of mutations in identified mutation pathways. Results: There was a discordance in the genetic aberrations detected among tumor versus cfDNA NGS tests, confirming intra-individual genetic diversity. Specifically, alterations in the DNA repair, PI3K, and epigenetic pathways were more common in tissue based testing (Table). Additionally, the median number of mutations identified was significantly lower for cfDNA based NGS testing (median 1.5) compared to tissue based NSG testing (median 10.0) (p < 0.0001). Conclusions: Discordance in the type of genomic aberrations in tissue versus cfDNA testing suggests intra-individual genetic diversity and may have implications in treatment selection when using these tests. Lower number of aberrations detected by the cfDNA testing may have occurred due to lower sensitivity of NGS by cfDNA compared to the tissue based NGS. The higher frequency of aberrations on tissue based testing suggests that tissue based testing should be used preferentially in clinical trials and practice. This data is hypothesis generating and needs further investigation in a larger cohort. [Table: see text]