An open label phase I/IIa study to evaluate the safety and efficacy of CCS1477 as monotherapy and in combination in patients with advanced solid/metastatic tumors

TPS5089

Background: CCS1477 is a potent, selective and orally bioavailable inhibitor of the bromodomain of p300 and CBP, two homologous and critical co-activators of the androgen receptor (AR) and its variant forms, including mutated, amplified and spliced AR, as well as c-Myc. CCS1477 represents a new therapeutic option for prostate cancer patients who have progressed after failure of anti-androgen therapy and in combination with anti-androgens such as enzalutamide or abiraterone. Methods: This is a Ph I/IIa study to determine the maximum tolerated dose (MTD) and/or recommended Phase II dose and schedule(s) of CCS1477 and investigate clinical activity of CCS1477 monotherapy and CCS1477 in combination with abiraterone or enzalutamide in patients with metastatic castration resistant prostate cancer (mCRPC). The trial aims to enrol approximately 150 patients and is currently recruiting in the UK with plans to open additional sites in the USA (NCT03568656). Key inclusion criteria (for the mCRPC) require previous treatment with abiraterone and/or enzalutamide, taxane as well as evidence of disease progression (PCWG-3 guidelines). Single dose and steady state pharmacokinetics will be determined along with changes in plasma PSA, LDH and ALKP and in circulating tumour cell number. Anti-tumour activity will be determined by standard imaging according to PCWG-3 guidelines. Paired tumour biopsies for biomarker assessment are being collected. Cohort 1 of the monotherapy dose-escalation (rolling 6 design; 3-6 patients/cohort) has completed. Enrolment to cohort 2 began in January 2019. Dose finding in combination (CCS1477 + abiraterone; CCS1477 + enzalutamide) will be open once monotherapy dose escalation completes. Following definition of a recommended phase 2 dose and schedule for monotherapy and in combination, three expansion arms in patients with mCRPC will be opened in parallel (25 patients/arm); CCS1477 monotherapy; CCS1477 + abiraterone; CCS1477 + enzalutamide. A further expansion in patients with advanced solid tumours with a mutation in p300 or CBP will also be opened. Clinical trial information: NCT03568656.

A phase Ib/II study of niraparib combination therapies for the treatment of metastatic castration-resistant prostate cancer (NCT03431350)

TPS5087

Background: Assessing multiple therapies in a single clinical trial can facilitate the rapid identification of new agents for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC). Niraparib (Nirap) is a highly selective PARP inhibitor, with potent activity against PARP-1 and PARP-2 deoxyribonucleic acid (DNA)-repair polymerases. PARP inhibition may be especially lethal in tumor cells with genetic DNA damage response deficits (DRD). Based on promising preclinical and clinical data, this study is designed as a master protocol with nirap as a backbone therapy. Combination 1 assesses the safety and efficacy of nirap plus JNJ-63723283 (JNJ-283), an anti-PD-1 monoclonal antibody. Combination 2 assesses nirap plus abiraterone acetate and prednisone (AA-P). Methods: This multicenter, global, open-label study is currently open at 18 sites in 5 countries of the planned XX sites, and is enrolling patients with mCRPC who have progressed on ≥1 androgen-receptor targeted therapy for mCRPC. Enrollment at time of abstract submission was 25 for combination 1. When combined with AA-P, the RP2D has been determined to be nirap 200 mg. The recommended phase-2 dose (RP2D) of nirap plus JNJ-283 was determined in Part 1 based on the incidence of specified adverse events and PK data to be 480 mg every 4 weeks. For Part 2 of the study, patients are assigned to receive oral niraparib daily plus JNJ-283 infusions once every four weeks until disease progression, unacceptable toxicity, death, study termination. Part 2 is described in the table. Clinical trial information: NCT03431350. [Table: see text]

First-in-human phase I and pharmacological study of TAS-119, a selective Aurora A (AurA) kinase inhibitor, in patients (pts) with advanced solid tumors

3063

Background: AurA is a serine threonine kinase regulating cell division and cell cycle progression and has a role in carcinogenesis. This clinical trial investigated safety, pharmacokinetics and -dynamics and antitumor activity of the selective oral AurA kinase inhibitor TAS-119. Methods: Pts with advanced solid tumors were enrolled into 6 dose escalation cohorts (70-300 mg BID 4 days on/3 days off; every 3 out of 4 weeks; or the same schedule in a continuous weekly schedule). In the expansion phase (intermittent schedule), pts with small-cell lung cancer (SCLC), breast cancer, or MYC-amplified/B-catenin mutated (MT) tumors were enrolled, and pts with other solid tumors in a basket cohort. Results: Overall, 34 pts were enrolled to the escalation (median age 67 years; 45.3% > 2 prior therapies); DLT was observed in 5 (16.1%) of 31 DLT evaluable pts; 1/10 at 150 mg, 1/6 at 200 mg, 1/5 at 250 mg, and 2/2 at 300 mg BID (fatigue, nausea, dry eyes, corneal epithelial microcysts). The maximum tolerated dose (MTD) was 250 mg BID and recommended Phase 2 dose (RP2D) was 200 mg BID. The most frequent treatment-emergent adverse events were diarrhea (28.3%), eye disorders (27%), fatigue (22.9%), and decreased appetite (14.8%). Grade 3 ocular toxicity were corneal epithelial microcysts in 1 pt (300 mg cohort) and punctate keratitis (expansion breast cancer cohort) in 1 pt. Toxicity grade ≥ 3 in ≥ 10% of pts were diarrhea (escalation part only), and increased lipase. Plasma exposure was dose-proportional and accumulation ratio was low. Pharmacodynamic data demonstrated target inhibition. Overall, 40 pts were enrolled to multiple expansions (10 SCLC, 9 breast cancer, 13 MYC-amp/B-cat MT tumors, 8 other; median age 60 years; 72.5% > 2 prior therapies). Median delivered relative dose intensity was 89.1% (47.9% - 100%). Stable disease was reported in 37.8% of patients but no complete or partial responses. Conclusions: TAS-119 demonstrated favorable safety and tolerability. Low-grade eye toxicity was a dose-dependent toxicity. Preliminary anti-tumor activity of monotherapy TAS-119 is limited. A Phase 1 trial combining TAS-119 with paclitaxel was conducted in parallel. Clinical trial information: NCT02448589.

TOPARP-B: A phase II randomized trial of the poly(ADP)-ribose polymerase (PARP) inhibitor olaparib for metastatic castration resistant prostate cancers (mCRPC) with DNA damage repair (DDR) alterations

5005

Background: We previously reported the antitumor activity of olaparib (400mg BID) against molecularly unselected mCRPC (TOPARP-A; Mateo et al NEJM 2015). We now report TOPARP-B, a phase II trial for patients with mCRPC preselected for putatively pathogenic DDR alterations. Methods: Patients with mCRPC progressing after ≥ 1 taxane chemotherapy underwent targeted sequencing of tumor biopsies and were deemed eligible when alterations (germline or somatic; mono- or bi-allelic) in any DDR gene were detected. Patients were randomized 1:1 under a “pick-the-winner” design to 400mg or 300mg of olaparib BID, aiming to exclude ≤30% response rate (RR) in either arm. The primary endpoint RR was defined as radiological response (RECIST 1.1) and/or PSA50% fall and/or CTC count conversion (Cellsearch; ≥5 to < 5), confirmed after 4-weeks. Analyses of RR per gene alteration subgroup was pre-planned. Secondary endpoints included progression-free survival (PFS), tolerability. Results: Overall, 98 patients (median age 67.6y) were randomized, with 92 patients treated and evaluable for the primary endpoint (70 RECIST-evaluable; 89 PSA50%-evaluable; 55 CTC-evaluable). All had progressed on ADT; 99% were post-docetaxel, 90% post-abiraterone/enzalutamide, 38% post-cabazitaxel. The overall RR was 54% (95%CI 39-69%, meeting threshold for primary endpoint) in the 400mg cohort and 37% (95%CI 23-53%) in the 300mg cohort. With a median follow-up of 17.6 months (mo), the overall median PFS (mPFS) was 5.4 mo. Subgroup analyses per altered gene identified indicated response rates for: BRCA1/2 of 80% (24/30; mPFS 8.1mo); PALB2 57% (4/7; mPFS 5.3mo); ATM 37% (7/19; mPFS 6.1mo); CDK12 25% (5/20; mPFS 2.9mo); others [ATRX, CHEK1, CHEK2, FANCA, FANCF, FANCG, FANCI, FANCM, RAD50, WRN] 20% (4/20; mPFS 2.8mo). The highest PSA50% response rates were observed in the BRCA1/2 (22/30; 73%) and PALB2 (4/6; 67%) subgroups. Conclusions: Olaparib has antitumor activity against heavily pre-treated mCRPC with DDR gene defects, with BRCA1/2 aberrant tumors being most sensitive but with confirmed responses in patients with other DDR alterations. Clinical trial information: NCT01682772.

Targeting IGF-1/2 with xentuzumab (Xe) plus enzalutamide (En) in metastatic castration-resistant prostate cancer (mCRPC) after progression on docetaxel chemotherapy (DCt) and abiraterone (Abi): Randomized phase II trial results

5030

Background: Insulin-like growth factor receptor-1 (IGF-1R) signaling activates the PI3K/AKT pathway and may lead to androgen receptor (AR) transactivation and progression to endocrine treatment resistance. Xe, an IGF-ligand-neutralizing antibody, binds to IGF-1 and IGF-2 and inhibits IGF-1R signaling. This multi-center randomized phase II trial (NCT02204072) evaluated anti-tumor activity of Xe plus En in mCRPC. Methods: Men with histologically/cytologically confirmed mCRPC and progression after DCt+Abi were randomized to receive Xe 1000mg IV QW + En 160mg/day oral, or En alone (28-day cycles until progression or intolerable adverse events [AEs]). Primary endpoint: progression-free survival by investigator assessment (PFS-IA); secondary: PFS by central review (PFS-CR), overall survival (OS), AEs. Results: Overall, 43 patients were randomized per arm; 70% Caucasian and 29% Asian (median age 70 y; range 46–88). At baseline (BL) the two arms were generally well balanced, although 33% v 47% were ECOG PS O, and 72% v 56% had a Gleason total score ≥8. By data cut-off (23 October 2017), 39/43 (Xe+En) and 38/43 patients (En) had discontinued, most due to disease progression. The median PFS-IA was 7.4 m for Xe+En (95% CI: 3.5–8.7) and 6.2 m for En (3.5–11.1) [HR = 0.99 (0.56–1.73); p = 0.96]. The results were similar after adjusting for BL ECOG PS and Gleason score. The median PFS-CR was 3.6 m for Xe+En (3.5–8.1) and 6.2 m for En (3.6–8.3) (HR = 1.22 [0.70–2.13]; p = 0.48). OS data are immature. For the two arms, prostate-specific antigen (PSA) response rates were 21% and 19%; maximum decline in PSA: -20 v -9 μg/L; PSA change at week 12: 19% v 18%; maximum decline in circulating tumor cells (CTC): -52% v -35%; and CTC response: 16% v 11%. The most frequently reported AEs were: fatigue 67% v 49%; decreased appetite 56% v 54%; weight reduction 37% v 12%; anemia 33% v 44%; back pain 30% v 37%. Nine patients discontinued Xe due to AEs. Conclusions: Addition of Xe to En did not prolong PFS in mCRPC compared with En alone. There were no notable differences in PSA-related endpoints and CTC between arms. Clinical trial information: NCT02204072.

Distinct radiological patterns of drug-induced pneumonitis (R-DIP) in early-phase clinical trials and predictive factors affecting outcome: A 10-year systematic review from the Royal Marsden Hospital Phase I Drug Development Unit experience

3088

Background: We studied clinical and radiological parameters influencing DIP in patients (pts) participating in phase I clinical trials, aiming to investigate predictive factors affecting DIP, in particular those affecting outcome. Methods: 2439 consecutive stage IV cancer pts on phase I clinical trials from 2007 to 2017 were identified. Pts with respiratory symptoms or abnormal lung imaging were reviewed in detail, with longitudinal analysis of imaging by an experienced radiologist. R-DIP was categorized according to internationally recognized criteria. Results: 60 pts developed R-DIP (overall incidence 2.5%); most frequent in pts receiving drug conjugates (31.1%) followed by targeted therapies (8.3%). Hypersensitivity pneumonitis was most common (33.3%) followed by non-specific interstitial pneumonitis (30%) and cryptogenic organising pneumonitis (26.7%). 45% pts who developed R-DIP were clinically asymptomatic. The number of affected lobes (OR 1.47, 95% CI: 1.19-1.81, p < 0.001) and the pattern of R-DIP (OR 5.83 for ARDS, 95% CI: 0.38-90.26, p = 0.002) were significantly associated with a higher CTCAE pneumonitis grading. 23% pts (14/60) had investigational medicinal product (IMP) temporarily discontinued or had a dose reduction while 42% pts (25/60) had IMP permanently discontinued. 48% pts were treated with steroids. The number of affected lobes, pattern of R-DIP and steroid therapy did not influence an improvement in R-DIP (p = 0.65, 0.27 and 0.23 respectively). Continuation of treatment resulted in worsening of DIP in 42.9% of cases. The only predictive factor for an improvement in DIP was an interruption of treatment (OR 0.05, 95% CI: 0.01-0.35, p = 0.01). 14 pts were retreated with a reoccurrence of R-DIP in 4 pts (28.6%). Conclusions: R-DIP from novel agents in early phase clinical trials presents in varied radiological patterns, with findings often preceding clinical symptoms. Treatment interruption leads to improvement of DIP and should be considered early. Close clinical and radiological surveillance is recommended should IMP be restarted.

External validation of a prognostic model for overall survival (OS) in men with metastatic castration-resistant prostate cancer (mCRPC)

5022

Background: We have previously developed and externally validated a prognostic model of OS in men with mCRPC treated with docetaxel (D), which included eight predictors: opioid analgesic use, ECOG performance status, albumin, disease site, LDH, hemoglobin, PSA, and alkaline phosphatase. We have used this model to develop prognostic risk groups. We sought to externally validate this model in a broader group of men with mCRPC and in specific subgroups (White, Black, Asian patients, different age groups) and to validate the two and three prognostic risk groups in this large dataset. Methods: Data from 5,790 mCRPC men randomized on 5 phase III trials were utilized to validate the prognostic model of OS: D +/- zibotentan (ENTHUSE), D +/- lenalidomide (MAINSAIL), D +/- dasatinib (READY), D+/- custirsen (SYNERGY), and tasquinimod/placebo)). We applied the estimated parameters from the prognostic model to each of the five data sets and computed a risk score. We assessed the predictive performance of the model by computing the time-dependent area under the receiver operating characteristic curve (tAUC) and validated the two-risk (low, high) and three-risk prognostic risk groups (low, intermediate, high) that were defined by the model. Results: The tAUC for the different groups is presented in the table. Race, age, and treatment subsets had similar results. For the two prognostic risk groups, the median OS in the low and high groups were 27.6 months (95% CI = 26.6-28.7) and 13.8 months (95% CI = 13.3-14.4). For the three prognostic risk group, median OS in the low, intermediate and high groups were 29.7 months (95% CI = 28.3-31.4), 19.0 month (95% CI = 18.3-20.4) and 12.1 months (95% CI = 11.5-12.9), respectively. Conclusions: This prognostic model for OS in men with mCRPC has been validated in a larger dataset, yields similar results across race, age and treatment groups. The model is robust and can be used to identify prognostic risk groups of patients for stratification and enrichment trials. Clinical trial information: NCT00626548. [Table: see text]

PIPA: A phase Ib study of selective ß-isoform sparing phosphatidylinositol 3-kinase (PI3K) inhibitor taselisib (T) plus palbociclib (P) in patients (pts) with advanced solid cancers—Safety, tolerability, pharmacokinetic (PK), and pharmacodynamic (PD) analysis of the doublet combination

3087

Background: Oncogenic hyperactivation of the PI3K pathway is common in multiple cancers, with preclinical data showing that CDK4/6 inhibitors sensitise PIK3CA mutant cancers to PI3K inhibitors. We report the activity of the P+T in solid tumors with PI3K pathway activation, along with the PD biomarker analysis. Methods: We previously reported the dose escalation phase identifying 125mg P given 3-weeks-on, 1-week-off in combination with T 2mg as the recommended phase 2 dose (R2PD, Lim, ASCO 2017). We report the results in solid tumors with confirmed activating mutations (mts) in the PI3K pathway, from dose escalation and expansion, with no prior exposure to CDK4/6 or PI3K pathway inhibitors. PD studies include analyses of platelet-rich plasma (PRP) and paired tumour biopsies. Results: 20 pts (median age 61, range 34-72) were treated at the doublet RP2D, M/F 7/13, with a median 4 prior treatments (range 2-11). Tumour types included colorectal, breast, lung, endometrial,oligodendroglioma and head and neck cancers. Durable disease control occurred in 3 patients with ER+ advanced breast cancer with responses lasting >6 months including 1 pt with a H1047R PIK3CAmt with an ongoing RECIST PR>36 cycles, 2 pts with PIK3CAmt colorectal cancer had RECIST SD for >5 months, and 1 patient with a PIK3CGmt anaplastic oligodendroglioma had clinical and radiological benefit lasting 5.5 months. Treatment was well tolerated with predictable G1-2 adverse events (AEs). G3 toxicities of neutropenia (n=6), thrombocytopenia (2), rash (2), mucositis (1) and raised transaminases (1 each) were all transient with no G4/5 AEs. Significant decreases in tumour pRb, and pAKT and pGSK3ß in PRP, confirmed modulation of both CDK4/6 and PI3K pathways at R2PD. Conclusions: Doublet P+T is well tolerated at the combination RP2D, with PD evidence of PI3K and CDK4/6 modulation in both plasma and tumor. Promising preliminary anti-tumor activity is seen in a mixed histology cohort selected for activating PIK3 mutations. Clinical trial information: NCT02389842.

PSMA heterogeneity and DNA repair defects in prostate cancer

5002

Background: Prostate-specific membrane antigen (PSMA) is a promising target for theranostics in metastatic castration resistant prostate cancer (mCRPC). Methods: Membranous PSMA (mPSMA) expression was immunohistochemically evaluated in castration sensitive (CSPC) (n = 38) and mCRPC (n = 60) tissue biopsies, and associations with molecular aberrations (next-generation sequencing; NGS) and clinical outcome were determined. Results: mPSMA expression was significantly higher (p = 0.005) in mCRPC biopsies (median H-score [interquartile range]; 55.0 [2.8-117.5]) compared to CSPC biopsies (17.5 [0.0-60.0]). Furthermore, patients with higher mPSMA expression ( > median H-score) at diagnosis had higher Gleason Grade (p = 0.04) and shorter OS (p = 0.006). Critically, 42% (16/38) of CSPC biopsies and 27% (16/60) of mCRPC biopsies were completely negative for mPSMA expression. In addition, CSPC and mCRPC biopsies expressing mPSMA demonstrated marked intra-tumor heterogeneity in expression levels, commonly exhibiting areas without detectable PSMA (CSPC – 100%; mCRPC – 84%), while heterogeneous mPSMA expression between metastases from the same patient was also observed. Subsequent genomic analysis showed that mCRPC patients with deleterious DNA damage repair (DDR) aberrations have higher (p = 0.016) mPSMA expression (87.5 [25.0-247.5]) than those without these (20 [0.3-98.8]). Furthermore, 9 of the 11 patients (82%) responding to PARP inhibition had a mPSMA H-Score above the median. The association between mPSMA expression and DDR aberrations was validated in an independent cohort with known DDR aberrations. Tumors with DDR aberrations had significantly higher mPSMA (ATM 212.5 [136.3-300] p = 0.005; BRCA2 300 [165-300] p = < 0.001) than unselected mCRPC biopsies (55.0 [2.75-117.5]). Finally, analyses of 122 mCRPC biopsy transcriptomes confirmed a negative correlation between PSMA and BRCA2 mRNA expression (p = 1.5x10-5). Conclusions: mPSMA expression in CSPC and mCRPC exhibits marked intra- and inter-patient heterogeneity, limiting the clinical utility of PSMA-targeted theranostics. We show for the first time that DDR gene aberrations associate with high mPSMA expression and may serve as predictive biomarkers for PSMA-targeted therapies.

Keynote-365 cohort a: Pembrolizumab (pembro) plus olaparib in docetaxel-pretreated patients (pts) with metastatic castrate-resistant prostate cancer (mCRPC)

145

Background: Activity with pembro or olaparib has been observed in mCRPC pts who progressed on 2nd-generation hormonal therapy (HT) and chemotherapy. From KEYNOTE-365 (NCT02861573), a phase 1b/2 umbrella study testing combinations in mCRPC, we report early results from cohort A combining pembro + olaparib. Methods: Pts with mCRPC were eligible if they progressed within 6 months prior to screening determined by either PSA progression or radiologic progression in bone or soft tissue. Pts were docetaxel-pretreated for mCRPC, may have received 1 other chemotherapy, and had ≤2 2nd-generation HT. Pts received pembro 200 mg IV Q3W + olaparib 400 mg orally twice daily. Primary end points: safety and PSA response rate (confirmed PSA decline ≥50%). Key secondary end points: ORR RECIST v1.1 (investigator review), disease control rate (DCR: CR+PR+SD ≥6 mo), time to PSA progression, composite response rate (ORR RECIST v1.1, confirmed PSA response, or confirmed decrease in circulating tumor cell count from ≥5 to <5 cells/7.5 mL blood), rPFS, and OS. Results: Median follow-up was 11 mo. 41 initiated treatment (median age 69 years; PD-L1+ 27%; visceral disease 42%; RECIST-measurable 68%; homologous recombination repair mutation [HRR] 0%). See efficacy in table below. Treatment-related AEs occurred in 39 (95%) pts. Most frequent (≥30%) were anemia (37%), fatigue (34%), and nausea (34%). Grade 3-5 treatment-related AEs were in 21 (51%) pts. There were 2 deaths; only 1 was treatment-related (cause unknown). Conclusions: Combination of pembro + olaparib has activity in pts previously treated with docetaxel and ≤2 2nd-generation HT for mCRPC and who are HRR wild type. Observed safety profile for the combination is consistent with individual profiles of pembro and olaparib. Clinical trial information: NCT02861573. [Table: see text]

Measurement science of the androgen receptor splice variant-7 protein in primary and castration-resistant prostate cancer tissue

151

Background: Liquid biopsies demonstrate the constitutively active androgen receptor splice variant-7 (AR-V7) associates with reduced benefit from endocrine therapies in castration resistant prostate cancer (CRPC). These studies provide little information pertaining to AR-V7 expression in PC tissue. Methods: AR-V7 protein expression was determined for 358 primary PC samples and 293 metastatic CRPC biopsies by immunohistochemistry. Associations with disease progression, full length AR (AR-FL) expression, response to therapy, gene expression, and circulating tumor cell (CTC) AR-V7 status were investigated. Results: AR-V7 protein is rarely expressed ( < 1% of 358 cases) in primary PC but is frequently detected (75% of 40 cases) following primary androgen deprivation therapy (ADT) alone (H-score 40; interquartile range 1.25-92.5), with a further significant (p = 0.020) increase following abiraterone or enzalutamide therapy (90; 20-150). In CRPC, AR-V7 expression is mainly nuclear (94% of 144 cases), correlates with AR-FL expression (p = < 0.001), and is homogeneous within single metastases (p = 0.997) but heterogeneous in different metastases from the same patient (p < 0.001). In addition, AR-V7 expression correlates with a 59-gene signature, including HOXB13, a co-regulator of AR-V7 function. Moreover, AR-V7 negative disease associates with better PSA response (p = 0.03) and overall survival (p = 0.02) from endocrine therapies. Finally, CTC+/AR-V7+ blood samples had significantly (p = 0.004) higher AR-V7 protein expression (100; 62.5-147.5) in paired tissue biopsy compared to CTC+/AR-V7- blood samples (15; 0.0-112.5), and AR-V7 protein expression is frequently detected (63% of 16 samples) in tissue of patients with CTC- blood samples. Conclusions: AR-V7 protein is not expressed until castration resistance and occurs after primary ADT alone. Levels of AR-V7 protein vary between metastases, and although AR-V7 associates with response to endocrine therapies, this suggests multiple resistance mechanisms exist in the same patient. If developed, agents targeting AR-V7 may be best explored earlier in the course of disease and in combination with other therapies.

Keynote-365 cohort C: Pembrolizumab (pembro) plus enzalutamide (enza) in abiraterone (abi)-pretreated patients (pts) with metastatic castrate resistant prostate cancer (mCRPC)

171

Background: Pembro has antitumor activity as monotherapy in pretreated advanced mCRPC (KEYNOTE-028; KEYNOTE-199). A study has suggested that pembro + enza after progression on enza may have clinical activity. KEYNOTE-365 (NCT02861573) is a phase 1b/2 umbrella study testing combinations in mCRPC; we report early results from cohort C combining pembro + enza in mCRPC. Methods: Patients who failed or became intolerant to ≥4 weeks of abi in the pre-chemotherapy mCRPC state were included. Pts also had to have progressed within 6 months prior to screening as determined by either PSA progression or radiologic progression in bone or soft tissue. Pts received pembro 200 mg intravenously Q3W with enza 160 mg per day orally, and response was evaluated by PSA levels Q3W and imaging Q9W for the first year and Q12W thereafter. Primary end points were safety and PSA response rate (confirmed PSA decline ≥50%). Key secondary end points were investigator-assessed ORR (RECIST v1.1), disease control rate (DCR: CR+PR+SD ≥6 mo), time to PSA progression, rPFS, and OS. Results: 69 pts initiated treatment (median age 69 years; PD-L1+ 30%; visceral disease 26%; measurable disease 36%). Median (95% CI) follow-up was 9 (7-13) mo. See efficacy outcomes in table. Treatment-related AEs occurred in 63 (91%) pts; most frequent (≥20%) were fatigue (30%), rash (23%), and nausea (22%). Grade 3-4 treatment-related AEs occurred in 28 (41%) pts; no deaths were due to treatment-related AEs. Conclusions: Early results from the pembro + enza combination show sustained activity in abi-pretreated frontline mCRPC. Observed safety profile for the combination treatment was consistent with the known safety profiles of pembro and enza. Clinical trial information: NCT02861573. [Table: see text]

The clinical impact of bone scan (BS) flare with enzalutamide (ENZA) in men with metastatic castration-resistant prostate cancer (mCRPC)

183

Background: Current PCWG3 guidelines for men with mCRPC define BS progression during therapy as requiring confirmation of new bone lesions that develop over time with additional new lesions. New unconfirmed BS lesions may reflect slow progression or a favorable osteoblastic reaction called a “BS flare” that can be misinterpreted as radiographic progression and lead to premature therapy discontinuation. The prevalence and clinical impact of BS flare is unknown for ENZA. Methods: We analyzed the association of BS flare with clinical outcomes and quality of life (QoL) in a retrospective analysis of two phase 3 trials of men with mCRPC treated with ENZA after (AFFIRM n = 1199) and before (PREVAIL n = 1717) docetaxel. Early and late BS flare was defined as new lesions on the first posttreatment BS (weeks 9-13) or subsequent BS, respectively, that were not confirmed to meet progression criteria on the next BS, while also requiring responding/stable PSA and soft-tissue disease. Results: Unconfirmed BS lesions were observed in 22% and 25% of stable/responding men receiving ENZA in AFFIRM and PREVAIL, respectively. Most BS flares were early, but late flares (week 17 or later) were seen in 2% and 13% of men, respectively. Unconfirmed BS lesions (early or late) had no impact on OS (HR 0.87; 95% CI 0.62-1.21) or rPFS (HR 0.91; 95% CI 0.58-1.44) in PREVAIL, but were associated with worse OS (HR 2.26; 95% CI 1.55-3.30) and rPFS (HR 1.73; 95% CI 1.33-2.26) in AFFIRM. Soft-tissue responses and PSA declines were more prominent in chemo-naïve men with unconfirmed BS lesions, which also had no impact on QoL or pain deterioration in either setting. Conclusions: BS flare occurred in ≈25% of responding men with mCRPC receiving ENZA and was not associated with adverse outcomes in chemo-naïve men. Our findings support the importance of avoiding premature treatment discontinuation in the presence of unconfirmed new BS lesions in the first 4 months of therapy. Worse outcomes associated with unconfirmed lesions in men post docetaxel illustrate the need for improved functional bone imaging in mCRPC and broader patient assessment to decide on treatment continuation. Clinical trial information: NCT00974311; NCT01212991.

TALAPRO-1: An open-label, response rate phase II study of talazoparib (TALA) in men with DNA damage repair (DDR) defects and metastatic castration-resistant prostate cancer (mCRPC) who previously received taxane-based chemotherapy (CT) and progressed on greater than or equal to one novel hormonal therapy (NHT)

TPS342

Background: There are no approved therapies for mCRPC that has progressed on taxane and NHT. Preclinical studies showed that DDR-positive prostate tumors may be sensitized to PARP inhibition. TALA inhibits PARP, causing cell death in BRCA1/2-mutated cells. Methods: This study (NCT03148795) is enrolling patients (pts) (N ≈ 100) with measurable soft tissue disease per RECIST v1.1, progressive mCRPC, DDR likely to sensitize to PARP inhibition, ECOG performance status ≤ 2, and no brain metastases, who received 1-2 CT regimens (including ≥ 1 taxane-based CT) and progressed on ≥ 1 NHT (enzalutamide/abiraterone acetate). Prior use of PARP inhibitors, cyclophosphamide, mitoxantrone, or platinum-based CT ≤ 6 mos before study or progression on a platinum-based CT at any time are excluded. Pts will receive TALA 1 mg/d orally (pts with moderate renal impairment, 0.75 mg/d) until radiographic progression, unacceptable toxicity, or withdrawal of consent. TALA should not be discontinued based on increased prostate specific antigen (PSA) or circulating tumor cell (CTC) count alone. Primary endpoint is best objective response (OR) rate (complete/partial soft tissue response; exact 2-sided 95% confidence interval). Responses must be confirmed ≥ 4 wks later by computed tomography/magnetic resonance imaging with no evidence of bone progression ≥ 6 wks later per PCWG3 criteria. Secondary endpoints include time to OR, duration of response, PSA decrease ≥ 50%, CTC count conversion (to CTC = 0 and < 5 per 7.5 mL of blood), time to PSA progression, radiographic progression-free survival, overall survival, safety, pt-reported outcomes, and pharmacokinetics of TALA. Efficacy will be assessed every 8 wks for the first 24 wks, then every 12 wks thereafter. An initial safety and efficacy analysis will be performed on 20 pts after ≥ 8 wks of treatment. An interim efficacy analysis is planned when 60 pts have completed ≥ 6 mos of treatment. This study was sponsored by Pfizer Inc. Previously presented at ESMO 2018, FPN 859TiP, De Bono JS et al. Reused with permission. Clinical trial information: NCT03148795.

Pembrolizumab for metastatic castration-resistant prostate cancer (mCRPC) previously treated with docetaxel: Updated analysis of KEYNOTE-199

216

Background: Previously presented data from cohorts (C) 1-3 of the phase 2 KEYNOTE-199 study (n = 258; NCT02787005) showed that pembrolizumab monotherapy had antitumor activity and acceptable safety in patients (pts) with mCRPC previously treated with next-generation hormonal agents (NHAs; eg, abiraterone, enzalutamide) and docetaxel. Activity was observed for both PD-L1–positive and negative cohorts and in RECIST-measurable and bone-predominant disease. We present data from KEYNOTE-199 C1, C2, and C3 based on longer-follow-up. Methods: C1 enrolled 133 pts with RECIST-measurable, PD-L1–positive disease, C2 enrolled 66 pts with RECIST-measurable, PD-L1–negative disease, and C3 enrolled 59 pts with nonmeasurable, bone-predominant disease. All pts had ECOG PS 0-2 and received ≥1 NHA and 1-2 prior chemotherapies including docetaxel. Pembrolizumab 200 mg Q3W was given for 35 cycles or until PD or intolerable toxicity. Response was assessed Q9W in yr 1, then Q12W. Primary end point was ORR per RECIST v1.1 by central review. Key secondary end points included DCR (CR + PR + SD ≥6 mo), duration of response (DOR), OS, and safety. Results: Median follow-up as of Aug 21, 2018, was 9.5 mo in C1, 7.9 mo in C2, and 14.1 mo in C3. ORR (95% CI) was 5% (2-11) in C1 and 3% ( < 1-11) in C2. DCR was 10% in C1, 9% in C2, and 22% in C3 per RECIST v1.1. Median (range) DOR was not reached (1.9-21.8+ mo) in C1 and 10.6 mo (4.4-16.8) in C2; KM estimates of DOR ≥12 mo were 71% and 50%. Median (95% CI) OS was 9.5 mo (6.4-11.9) in C1, 7.9 mo (5.9-10.2) in C2, and 14.1 (10.8-17.6) in C3. 12-mo OS rates were 41% in C1, 35% in C2, and 62% in C3; 18-mo rates were 30%, 21%, and 36%. Grade 3-5 drug-related AE rates were 15% in C1, 14% in C2, and 17% in C3. There were 2 drug-related deaths (n = 1 each sepsis and pneumonitis). Conclusions: Pembrolizumab shows antitumor activity and disease control with acceptable safety in RECIST-measurable and bone-predominant mCRPC previously treated with NHAs and docetaxel. Responses are durable, and the observed OS benefit is promising. Clinical trial information: NCT02787005.

Assessment of circulating tumor cell number as a transitional surrogate endpoint for survival in phase II trials for metastatic castration-resistant prostate cancer

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Background: Short-term measures of response that reflect clinical benefit are a critical unmet need for clinical trials for mCRPC. Using data from 5 randomized mCRPC trials, we showed that a response endpoint (RE) based on a change in CTC number using the FDA cleared CellSearch® (Menarini) platform from any, (≥ 1, CTC any) to 0 (CTC0) per 7.5 ml of blood was associated strongly with overall survival (OS). Here we explored whether different CTC and PSA REs could serve as “transitional surrogates” defined as a biomarker validated in phase 2 but not in phase 3 trials for overall survival (OS), using the baseline and week 13 prostate-specific antigen (PSA) level and CTC counts. Methods: Four 13-week REs were studied: (i) PSA50 (≥ 50% PSA decline from baseline), (ii) CTC0 (≥ 1 CTC/7.5 ml of blood at baseline and 0 CTCs at week 13), (iii) both PSA50 and CTC0, and (iv) either PSA50 or CTC0. The relative effectiveness of these REs as transitional surrogates for OS was evaluated at the patient level by discrimination, the separation between responder and non-responder survival curves, and at the trial level using explained variation, the accuracy in predicting k-month survival in a trial with the response proportion. Results: A total of 6081 pts were enrolled of whom 5660 (93%) survived until week 13 and among these patients 3080 (54%) had a baseline CTC count ≥ 1 and baseline PSA ≥ 5 ng/ml. At the patient level, separation between responder and non-responder survival curves over time was greater using CTC0 than PSA50 (average difference in survival probability 0.35 vs. 0.29, respectively). At the trial level, explained variation in survival over time was also greater for CTC0 than PSA50 (average R-squared 0.67 vs. 0.58, respectively). CTC/PSA combination REs did not improve on CTC0 at either level. Conclusions: The CTC0 RE provides stronger discrimination than PSA50 at the patient level and greater observed explained variation at the trial level. The results suggest that for the individual patient, a decrease in CTCs to zero at week 13 is a stronger indicator of longer term OS than the more widely used PSA50 and serves as a reasonably likely surrogate for OS in clinical trials.

Clinical validation of circulating cytokines as markers of prognosis and response to docetaxel in men with metastatic castration-resistant prostate cancer

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Background: Elevated circulating macrophage inhibitory cytokine -1 /growth differentiation factor 15 (MIC-1/GDF15), interleukins 4 (IL4) and 6 (IL6) levels were associated with poor prognosis and resistance to docetaxel chemotherapy in an exploratory cohort of men with metastatic castration resistant prostate cancer (mCRPC). To establish level 2 evidence of biomarker utility, these cytokines were tested in internal and external validation cohorts. Methods: Internal validation cohort: Plasma samples taken at baseline (BL) and preC2 docetaxel (n = 120). MIC-1/GDF15, IL-4 and IL-6 measured by ELISA assay. External validation cohort: Serum samples taken at BL and/or preC3 docetaxel in 430 men with mCRPC on phase III SYNERGY study (docetaxel +/- custirsen as 1st line chemotherapy in mCRPC with no OS benefit in the experimental arm). MIC-1/GDF15 measured by ELISA assay. Associations between cytokine levels, PSA response, time to PSA progression and OS were assessed by non-parametric tests and Cox Regression survival analyses. Results: Internal validation: At a median follow-up of 14 months, higher MIC-1/GDF15 levels at BL and preC2 were associated with shorter OS (BL; HR 1.2 95%CI 1.0-1.4; p = 0.03 and preC2; HR 1.3 95%CI 1.1-1.5; p = 0.004). Increase in MIC-1/GDF15 after chemotherapy correlated with lack of PSA response (p < 0.001). IL4 and IL6 did not correlate with survival or demonstrate additional value. External validation: At a median follow-up of 23 months, higher MIC-1/GDF15 levels at BL and preC3 predicted shorter OS (BL; HR 1.4 95%CI 1.2-1.6; p < 0.0001 and preC3; HR 1.6 95%CI 1.3-1.8; p < 0.0001). Higher pre C3 MIC-1/GDF15 levels were also associated with shorter time to PSA progression (HR 1.2 95% CI 1.0-1.4; p = 0.02). Rise in MIC-1/GDF15 from BL to preC3 correlated with lack of 50% PSA fall at 12 weeks (p < 0.001). Conclusions: Adherence to a biomarker development pipeline provides level 2 evidence of the prognostic value of circulating MIC-1/GDF15 in men with mCRPC receiving docetaxel. A prospective biomarker led study is now necessary to establish clinical utility.

Overall Survival of Black and White Men With Metastatic Castration-Resistant Prostate Cancer Treated With Docetaxel

PURPOSE

Several studies have reported that among patients with localized prostate cancer, black men have a shorter overall survival (OS) time than white men, but few data exist for men with advanced prostate cancer. The primary goal of this analysis was to compare the OS in black and white men with metastatic castration-resistant prostate cancer (mCRPC) who were treated in phase III clinical trials with docetaxel plus prednisone (DP) or a DP-containing regimen.

METHODS

Individual participant data from 8,820 men with mCRPC randomly assigned in nine phase III trials to DP or a DP-containing regimen were combined. Race was based on self-report. The primary end point was OS. The Cox proportional hazards regression model was used to assess the prognostic importance of race (black v white) adjusted for established risk factors common across the trials (age, prostate-specific antigen, performance status, alkaline phosphatase, hemoglobin, and sites of metastases).

RESULTS

Of 8,820 men, 7,528 (85%) were white, 500 (6%) were black, 424 (5%) were Asian, and 368 (4%) were of unknown race. Black men were younger and had worse performance status, higher testosterone and prostate-specific antigen, and lower hemoglobin than white men. Despite these differences, the median OS was 21.0 months (95% CI, 19.4 to 22.5 months) versus 21.2 months (95% CI, 20.8 to 21.7 months) in black and white men, respectively. The pooled multivariable hazard ratio of 0.81 (95% CI, 0.72 to 0.91) demonstrates that overall, black men have a statistically significant decreased risk of death compared with white men ( P < .001).

CONCLUSION

When adjusted for known prognostic factors, we observed a statistically significant increased OS in black versus white men with mCRPC who were enrolled in these clinical trials. The mechanism for these differences is not known.

Scanning Electron Microscopy of Circulating Tumor Cells and Tumor-Derived Extracellular Vesicles

To explore morphological features of circulating tumor cells (CTCs) and tumor-derived extracellular vesicles (tdEVs), we developed a protocol for scanning electron microscopy (SEM) of CTCs and tdEVs. CTCs and tdEVs were isolated by immunomagnetic enrichment based on their Epithelial Cell Adhesion Molecule (EpCAM) expression or by physical separation through 5 μm microsieves from 7.5 mL of blood from Castration-Resistant Prostate Cancer (CRPC) patients. Protocols were optimized using blood samples of healthy donors spiked with PC3 and LNCaP cell lines. CTCs and tdEVs were identified among the enriched cells by fluorescence microscopy. The positions of DNA+, CK+, CD45- CTCs and DNA-, CK+, CD45- tdEVs on the CellSearch cartridges and microsieves were recorded. After gradual dehydration and chemical drying, the regions of interest were imaged by SEM. CellSearch CTCs retained their morphology revealing various shapes, some of which were clearly associated with CTCs undergoing apoptosis. The ferrofluid was clearly distinguishable, shielding major portions of all isolated objects. CTCs and leukocytes on microsieves were clearly visible, but revealed physical damage attributed to the physical forces that cells exhibit while entering one or multiple pores. tdEVs could not be identified on the microsieves as they passed through the pores. Insights on the underlying mechanism of each isolation technique could be obtained. Complete detailed morphological characteristics of CTCs are, however, masked by both techniques.

Safety, efficacy and survival of patients with primary malignant brain tumours (PMBT) in phase I (Ph1) trials: the 12-year Royal Marsden experience

BACKGROUND

Primary malignant brain tumours (PMBT) constitute less than 2% of all malignancies and carry a dismal prognosis. Treatment options at relapse are limited. First-in-human solid tumour studies have historically excluded patients with PMBT due to the poor prognosis, concomitant drug interactions and concerns regarding toxicities.

METHODS

Retrospective data were collected on clinical and tumour characteristics of patients referred for consideration of Ph1 trials in the Royal Marsden Hospital between June 2004 and August 2016. Survival analyses were performed using the Kaplan-Meier method, Cox proportional hazards model. Chi squared test was used to measure bivariate associations between categorical variables.

RESULTS

100pts with advanced PMBT were referred. At initial consultation, patients had a median ECOG PS 1, median age 48 years (range 18-70); 69% were men, 76% had glioblastoma; 68% were on AEDs, 63% required steroid therapy; median number of prior treatments was two. Median OS for patients treated on a Ph1 trials was 9.3 months (95% CI 5.9-12.9) versus 5.3 months (95% CI 4.1-6.1) for patients that did not proceed with a Ph1 trial, p = 0.0094. Steroid use, poor PS, neutrophil-to-lymphocyte ratio and treatment on a Ph1 trial were shown to independently influence OS.

CONCLUSIONS

We report a survival benefit for patients with PMBT treated on Ph1 trials. Toxicity and efficacy outcomes were comparable to the general Ph1 population. In the absence of an internationally recognized standard second line treatment for patients with recurrent PMBT, more Ph1 trials should allow enrolment of patients with refractory PMBT and Ph1 trial participation should be considered at an earlier stage.

Overall survival between African-American (AA) and Caucasian (C) men with metastatic castration-resistant prostate cancer (mCRPC)

LBA5005

Background: Reports have suggested that African-American (AA) men with metastatic castration-resistant prostate cancer (mCRPC) have shorter overall survival (OS) than Caucasian (C) men. Prior reports have been limited by small sample size. The primary goal of this analysis was to compare OS in AA men to Caucasian men treated with docetaxel/prednisone or a docetaxel/prednisone containing regimen. Methods: Individual patient data from 8,871 mCRPC men randomized on nine phase III trials to docetaxel/prednisone (DP) or a DP containing regimen were combined. Race used in the analysis was based on self-report. The primary endpoint is OS, defined as the time between randomization and death or date of last follow-up if patients were alive. The proportional hazards model was used to assess the prognostic importance of race (AA vs. C) adjusting for established risk factors that were common across the trials (age, PSA, performance status, alkaline phosphatase, hemoglobin, and sites of metastases). Results: Of 8,871 patients, 7,528 (85%) were C, 500 (6%) were AA, 424 were Asian (5%) and 419 (4%) had race unspecified. The last two groups were deleted from the analysis leaving 8,452 pts. Median age was 69 years and 94% had performance status 0-1. Median hemoglobin, PSA and alkaline phosphatase were 12.9 g/dL, 86 ng/mL and 139 U/L, respectively. Pattern of metastatic spread were: 72% bone disease with or without lymph nodes, 9% lung disease, 9% liver disease and 7% lymph nodes only. Median OS were 21.0 (95% CI = 19.4-22.5) vs. 21.2 months (95% CI = 20.8-21.7) in AAs and C, respectively. In multivariable analysis adjusting for established risk factors, the pooled hazard ratio (HR) for AAs vs. Caucasians was 0.81 (95% CI = 0.72-0.92, p-value = 0.001) in all patients. Similar results were observed in 4,172 of patients who were treated with DP. Conclusions: We observed a statistically significant increased OS in AA vs. C men with mCRPC who were eligible to be enrolled on these clinical trials. Further understanding the biological variation by race in men with mCRPC treated with DP is warranted.