Prognostic biomarkers and clinical outcomes in neuroendocrine prostate cancer (NEPC)

209

Background: NEPC includes both pure small cell carcinoma and mixed tumors with varying degrees of adenocarcinoma and neuroendocrine histology. It arises de novo or is treatment associated (TA) post androgen deprivation therapy. Clinical outcome data and prognostic biomarkers are limited and were thus explored. Methods: Patients with high grade prostate cancer and morphologic and/or immunohistochemical (IHC) NEPC features were included in this retrospective multicentre study. Clinical stage, Gleason score, and serum biomarkers were recorded. Kaplan-Meier method and log-rank test calculated and compared overall survival (OS) from time of NEPC diagnosis.Cox proportional hazards regression assessed prognostic impact of serum biomarkers at diagnosis and de novo vs TA status, adjusting for clinical stage and castration resistance. Results: 135 NEPC cases were identified. 124 (92%) were mixed tumors. 56 (41%) arose de novo. 79 (59%) were TA. 77% of those with a Gleason score (N=85/110) were grade group 5. Median PSA pre-NEPC biopsy was 11.6 ng/mL. At NEPC diagnosis, 19 (14%) had localized disease (median OS 123.0 mo); 33 (24%) non-metastatic castrate-sensitive disease (median OS 42.3 mo); 6 (4%) non-metastatic castrate-resistant disease (median OS 14.3 mo); 35 (26%) metastatic castrate-sensitive disease (median OS 17.6 mo); and 42 (31%) metastatic castrate-resistant disease (median OS 9.6 mo). Median OS for those with visceral metastases was 8.6 mo (95% CI 6.0 – 14.6), compared to patients with non-visceral metastases (11.1 mo; 95% CI 13.7 – 21.5) and no metastases (42.3 mo; 95% CI 47 – 89). Anemia (adjusted HR 1.66; 95% CI 1.05 - 2.16, p = 0.031) and NLR >3 (adjusted HR 1.51; 95% CI 1.01 - 2.52, p = 0.045) were associated with increased risk of death. De novo disease, elevated LDH, serum PSA, and Gleason score were not prognostic. Conclusions: This study identifies NEPC clinical outcomes by stage, with survival poorer than expected in pure prostate adenocarcinoma. Anemia and elevated NLR >3 are prognostic biomarkers that may help risk stratify and guide treatment intensification, including platinum-based chemotherapy. Further biomarker characterization of NEPC through IHC-staining pattern and genomic analysis is currently underway by this group.

Prospective ctDNA genotyping for treatment selection in metastatic castration-resistant prostate cancer (mCRPC): The Canadian Cancer Trials Group phase II PC-BETS umbrella study

218

Background: Precision oncology trials in mCRPC rely on genomic profiling of tumor tissue but testing failure rates are 30-40%. Incorporating liquid biopsy screening into trial designs may address limitations of tissue-only genotyping. We report findings from the first 500 plasma samples screened on Prostate Cancer Biomarker Enrichment and Treatment Selection (PC-BETS), a phase II multicenter, eight-arm Canadian umbrella trial (NCT03385655) using circulating tumor DNA (ctDNA) to match mCRPC patients to biomarker (BM)-informed targeted therapies. Methods: mCRPC patients previously treated with novel androgen receptor inhibitor therapy were eligible after PSA and/or radiological progression. Plasma cell-free DNA and matched leukocyte DNA underwent deep targeted sequencing with an exon-limited panel (Feb 2017-Sep 2020), or an expanded panel integrating select introns and a genome-wide copy number grid (July 2020-present). A molecular tumor board (MTB) assigned patients to treatment arms based on prespecified BM criteria (BM+), or by randomization if BM negative (BM-). The primary endpoint was clinical benefit rate (PSA50 response; RECIST CR/PR; or SD ≥12 weeks). We report tumor content (ctDNA%), genomic alterations, and BM status for the whole cohort. Results: As of Nov 2021, 503 samples were screened from 444 patients, with 496 passing quality control. 345 samples (70%) had ctDNA ≥1% (ctDNA+), of which the median ctDNA fraction was 20% (IQR 6-44%). 72% of ctDNA+ samples were BM+ (52% of all screened samples). Driver alterations influencing BM status included AR (76%; 59% gain, 24% mutation), PI3K pathway (37%; PTEN 30%, PIK3CA 6%, AKT 3%), and DNA repair defects (26%: mismatch repair 5%, BRCA2 7%, ATM 6%, CDK12 7%, other 6%). The expanded panel detected additional intronic structural variants in baseline ctDNA+ samples ( PTEN 1% vs 25%; BRCA2 0.6% vs 5%; AR 16% vs 37%), and identified whole genome doubling and segmental deletion events. To date, 167 patients have been enrolled to a substudy (83 BM+, 84 BM-). Median time from blood draw to MTB decision improved over time (first vs second half of screening period: 28 vs 17d) with implementation of optimized lab workflows, standardized genomic reports, and hierarchical genomic eligibility assessment. As of Sep 2022, 485 patients have been screened (updated results will be presented). Conclusions: Prospective centralized screening of ctDNA is feasible for guiding precision oncology initiatives. Improvements to assay design, robust availability of targeted therapies and an adaptive approach to biomarker assessment allowed high detection of actionable tumor alterations. Our framework can be used in future trials to stratify patients according to genomic alteration status. Study accrual to PC-BETS is ongoing, with a screening target of 600 patients. Clinical trial information: NCT02905318, NCT03385655 .

Outcomes of first subsequent taxane (FST) therapy in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) who previously received docetaxel intensification (DI) for metastatic castration-sensitive prostate cancer (mCSPC)

72

Background: The management of advanced prostate cancer continues to rapidly evolve, particularly with earlier use of survival prolonging therapies in mCSPC. Though approved prior to the use of intensification therapy in mCSPC, taxane-based chemotherapies remain a relevant option for pts with mCRPC. However, there is little evidence determining outcomes of taxane chemotherapies as FST in mCRPC pts who received DI in mCSPC. The purpose of this study is to compare outcomes between the survival prolonging taxanes, docetaxel (D) and cabazitaxel (C), as FST after DI. Methods: New patient consults seen at the Cross Cancer Institute from 1 July 2014 to 31 Dec 2020 were reviewed. Pts were considered eligible if they received DI for mCSPC and then received either D or C in mCRPC. Variables of interest were collected from the electronic medical record. The primary endpoint was ≥50% PSA response at 12 weeks relative to baseline for FST. Secondary endpoints included OS from mCSPC diagnosis, as well as PFS and OS from FST start date. PSA responses were compared using chi-squared test and time-based endpoints were compared using the Kaplan-Meier method. Results: 34 pts were identified: D = 22, C = 12 as FST. 91.2% of pts (D 95.5% vs C 83.3%) received FST in 2nd line mCRPC. Median age at diagnosis (63.1 vs 67.1 yrs, p = 0.236) and median time to CRPC (18.6 vs 14.2 mos, p = 0.079) were similar for D and C, respectively. Median time to FST (24.1 vs 34.6 mos, p = 0.036) and OS from mCSPC diagnosis (30.9 vs 52.7 mos, p = 0.002) were significantly shorter for pts receiving C vs D. PSA responses occurred in 40.9% of pts treated with D compared to 25.0% treated with C (p = 0.645). There was no significant difference in median PFS (2.7 vs 3.5 mos, p = 0.727) or median OS (11.4 vs 8.1 mos, p = 0.132) from time of FST for pts treated with D vs C, respectively. Conclusions: Both D and C demonstrated activity as FST after DI in mCSPC. Pts who received C had shorter time to FST and OS from mCSPC. The reasons for this may reflect clinician preference for C in pts with aggressive or rapidly progressing disease. No difference was found in PSA response, PFS, or OS from FST with D compared to C. While limited by its retrospective nature and small sample size, this study suggests that D is active as FST despite treatment with DI in mCSPC.

Comparative outcomes of metastatic prostate cancer (mPC) patients (pts) with DNA damage response gene alterations (DDR-a): A single-center experience

169

Background: DDR-a are prevalent in mPC pts. The clinical behaviour of these pts is not well defined. We sought to investigate how DDR-a affects prognosis and treatment outcomes in mPC pts. Methods: Eligible pts were age ≥18 with mPC who had undergone germline (G) and/or somatic (S) next generation sequencing (NGS) at the Cross Cancer Institute 2016-2021. Pts were considered DDR-a if a pathogenic/likely pathogenic variant (P/LP-v) in a DDR gene was identified on G or S NGS; patients were considered DDR-p if no P/LP-v was identified on S NGS. Data from electronic medical records were collected. The primary endpoint was overall survival (OS) from diagnosis of mPC. Secondary endpoints included: OS and progression free survival (PFS) from initial diagnosis of prostate cancer (PC); PSA response after 12 weeks, and PFS and OS from the start time of 1st and 2nd line therapies. Time based endpoints were analyzed using the Kaplan-Meier (KM) method, and log-rank statistics were used to compare the KM curves. PSA responses were compared using chi-squared testing. Results: 23 DDR-a and 48 DDR-p pts were identified. The most frequent DDR-a were BRCA2 (n=11) and ATM (n=6). Baseline characteristics including age at diagnosis were similar between the two groups. 1st line systemic therapy was androgen deprivation therapy (ADT) alone in 73.9% of DDR-a and 77.0% of DDR-p. 2nd line therapy was abiraterone or enzalutamide in 65% of DDR-a and 92% of DDR-p. Olaparib was received by 52% of DDR-a pts. No difference in OS from mPC (65.7 vs 51.0 mos, p=0.487), OS from initial diagnosis (94.1 vs 88.9 mos, p=0.865), PFS on 1st line therapy (33.2 vs 31.0 mos, p=0.847), OS on 1st line therapy (85.6 vs 78.6 mos, (p=0.799) PFS on 2nd line therapy (8.4 vs 13.1 mos, p=0.569) or OS on 2nd line therapy (32.5 vs 35.8 mos, p=0.901) was seen for DDR-a vs DDR-p, respectively. PSA responses to 1st and 2nd line therapies were similar and will be presented as waterfall plots. Conclusions: In this single-center cohort, no difference in clinical characteristics or outcomes were seen in DDR-a compared to DDR-p pts. While this study is limited by small numbers and retrospective nature, it adds to the growing literature characterizing the clinical behaviour of DDR-a mPC. Collaborative efforts are required to better define this molecular cohort of pts.

Real-world management of metastatic castration-resistant prostate cancer (mCRPC): A national multicenter cohort study

252

Background: The management of patients with mCRPC has evolved since the introduction of androgen-receptor axis targeted agents (ARATs). The Genitourinary Research Consortium (GURC) initiated a prospective, phase 4, multicentre, non-interventional, longitudinal cohort study of Canadian men with advanced prostate cancer to determine real-world treatment patterns and outcomes. Methods: 25 sites across Canada participated in this study including patients managed by urologists, medical- and radiation-oncologists between 2018 to 2021. Baseline patient characteristics and mCRPC treatment patterns are reported here. Treatment patterns reviewed included time to second-line treatment use and time to progression or death. Results: 136 mCRPC patients were enrolled. Median age was 73 years (range 66 to 80) with 54 (40%) having a Gleason score of >8 at diagnosis. Median PSA at enrollment was 8.9 (2.4 to 25.1) ng/ml. At study entry, 90/132 (66%) patients with mCSPC and 42/132 (31%) patients nmCRPC had progressed to develop mCRPC. One hundred and twenty-one (89%) of patients in this cohort received first-line treatment for mCRPC, the most common was abiraterone acetate + prednisone in 67 (49%) and enzalutamide in 41 (30%), followed by docetaxel in 6 (4.4%), and Radium-223 in 5 (3.7%) patients. During the 25-month median follow-up period (range 6-28), 59 (49%) of the patients receiving first line mCRPC therapy had documented disease progression or death. At the time of last recorded follow-up, 37 (28%) patients who progressed received a second-line therapy for mCRPC. Median time to progression in this cohort was 21 months (95% CI: 15.2 - NE), with ARAT-to-ARAT being the most common sequencing pattern observed in 15 (39%) patients, followed by ARAT to chemotherapy in 14 (37%). Conclusions: In this real-world analysis of mCRPC patients, ARAT therapy was the preferred approach for first-line treatment intensification in over 108 (80%) patients. Despite evidence of poor response rates, ARAT-to-ARAT was the most common sequencing for second line therapy, followed by ARAT-to-chemotherapy treatment. Further analysis and follow-up will help define optimal mCRPC management, in real world setting.

Evolving real-world patterns of practice in metastatic castration-sensitive prostate cancer (mCSPC): The genitourinary research consortium (GURC) national multicenter cohort study

86

Background: Treatment options for patients with mCSPC have rapidly evolved with the introduction of androgen receptor axis targeted therapies (ARATs) and chemotherapy. The GURC cohort study is a phase 4, multicentre, non-interventional, longitudinal cohort study of Canadian men with advanced prostate cancer. We prospectively examined the evolving real world management and treatment patterns of patients with mCSPC, with a focus on treatment intensification beyond ADT and germline DNA damage repair (DDR) testing. Methods: Clinical management patterns, baseline patient characteristics, germline DDR alteration status, treatment intensification with ARATs (abiraterone acetate [AA], apalutamide [Apa], enzalutamide [Enza]) and chemotherapy within the mCSPC cohort were analyzed. Results: 204 patients with mCSPC were enrolled from 2018 to 2021 across 25 Canadian sites. The median age was 71 (range 64 - 77), median PSA at study entry was 24, 88% (158/180) of patients had de novo mCSPC, 69% (110/204) of patients had a Gleason Score > 7, and 4% (2/49) of the patients who received a germline testing harbored a germline DDR alteration (BRCA2 = 1, MUTYH/MEN1 = 1). The distribution of high and low volume mCSPC at study entry was 62% (118/189) and 37% (71/189), respectively. Overall, patients received ADT alone 27% (51/189), AA 45% (86/189), apalutamide 17% (33/189), docetaxel 8% (15/189), and enzalutamide 3% (6/189). Treatment intensification with ARATs/docetaxel was administered to 69% [141/189]) of patients. Patients treated with ADT alone had a significantly lower volume of disease at treatment initiation (low volume rates of 49% [24/49] in ADT alone vs 33% [47/143] in treatment intensified patients, p = 0.044). Among those receiving treatment intensification with ARATs/docetaxel, time to intensification was ≤ 3 months in 78.5 % (113/144). Conclusions: This cohort study demonstrates that patients with mCSPC continue to receive ADT alone and docetaxel over time, despite an ever-increasing list of accessible ARATs. Patients receiving ADT alone appear to have lower volume of disease. Germline DDR testing is not yet comprehensively performed. This underlines the real world need to provide greater education and resources to encourage ARAT treatment and genetic testing in this setting.

Analysis of the role of PI3K-AKT and DNA damage repair (DDR) genomic biomarkers as predictors of clinical outcomes in nonmetastatic castration-resistant prostate cancer (nmCRPC)

175

Background: Clinically relevant outcomes in nmCRPC treated with androgen receptor-axis-targeted therapies (ARAT) may be inferior in patients with tumors harboring mutations bypassing androgen receptor signalling. This final update of a retrospective, multicenter analysis explores the association between genomic mutations in the PI3K-AKT and DDR signalling pathways with ARAT treatment outcomes in nmCRPC patients. Methods: Relevant clinical endpoint were collected for high-risk nmCRPC patients treated with an ARAT at APCaRI affiliated cancer centers, including median metastasis-free survival (MFS), overall survival (OS), PSA decline ≥ 50% (PSA50), and second progression free survival (PFS2). Archival tumor tissue was accessed for next generation gene sequencing, examining for genomic alterations in 500 genes, including those involved in the DDR and the PI3K-AKT signalling pathways. Comparison of outcomes of patients with DDR and PI3K-AKT pathway mutations was conducted using Cox proportional hazards regression using wildtype cases as the reference group, adjusting for PSA doubling time and pelvic lymphadenopathy. Results: Of the 37 patients included, 30 (82%) received apalutamide, 5 (13%) received darolutamide, and 2 (6%) received enzalutamide. 10 patients (27%) had PI3K-AKT pathway mutations (4 PTEN, 3 PIK3Ca, 2 PIK3C2G, 1 PIK3C2b), 8 patients (22%) had DDR gene mutations (3 ATM, 2 CHEK1, 1 BRCA2, 1 CDK12, 1 CHEK2, 1 FANCD2, 1 FANCL), and 1 patient (3%) had 2 MLH1 mutations (microsatellite instability). Of those who had subsequent treatment, 1 received enzalutamide and 5 received abiraterone. Patients with PI3K-AKT pathway mutations had significantly shorter MFS (4.8 mo; HR 4.2; 95% CI 1.2 – 15.0; p = 0.025). Those with DDR mutations had a trend towards shorter MFS (23.3 mo HR 3.7; 95% CI 0.71 – 13.4; p = 0.134). OS data remains immature. 4 (11%) patients did not achieve PSA50, including a patient with 2 MLH1 mutations. Conclusions: This final analysis demonstrates that nmCRPC with PI3K and DDR signalling pathway mutations have poor clinical outcomes when treated with ARAT, likely secondary to decreased reliance on the androgen receptor signalling pathway. These results highlight the potential value of exploring targeted therapies, such as PARP or AKT inhibitors in patients with these mutations.

Exploratory gene-by-gene analysis of olaparib in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC): PROfound

126

Background: The Phase 3 PROfound trial (NCT02987543) met its primary endpoint and key secondary endpoints, including improved overall survival (OS) for olaparib in men with mCRPC with alterations in BRCA1, BRCA2, or ATM (Cohort A). We report gene-by-gene analysis of olaparib antitumor activity among the 15 prespecified homologous recombination repair (HRR) genes. Methods: Pts were randomized to olaparib (300 mg bid; n=256) or physician’s choice of enzalutamide or abiraterone (control; n=131). Exploratory analyses in pts with alterations in BRCA1 and/or BRCA2 (BRCA, regardless of co-occurring alterations with other HRR genes) or in single genes were conducted. Results: Evidence of olaparib antitumor activity was observed in subgroups with >10 pts (table). Data for pts with alterations in only BRCA1, BRCA2, PPP2R2A, RAD51B, RAD54L, PALB2, BRIP1, CHEK1, BARD1, and RAD51D will be reported (no FANCL or RAD51C enrolled). Conclusions: Small subgroups limit interpretation for some genes. Olaparib antitumor activity is greatest in pts with BRCA alterations, with a spectrum of clinical sensitivity to olaparib as defined by rPFS and OS across the broader population with alterations in other HRR genes. Clinical trial information: NCT02987543. [Table: see text]

KEYNOTE-365 cohort B: Pembrolizumab (pembro) plus docetaxel and prednisone in abiraterone (abi) or enzalutamide (enza)–pretreated patients with metastatic castration-resistant prostate cancer (mCRPC)—New data after an additional 1 year of follow-up

10

Background: For men with mCRPC, systemic therapies such as docetaxel and cabazitaxel improve survival, but more effective treatments are needed. KEYNOTE-365 (NCT02861573) is a phase 1b/2 study to examine the safety and efficacy of pembro in combination with 4 different study medications (cohorts A, B, C, D) in mCRPC. Previous data from cohort B with a median of 20 months of follow-up showed that pembro + docetaxel and prednisone was well tolerated and had antitumor activity in patients (pts) with mCRPC previously treated with abi or enza. New efficacy and safety data after an additional year of follow-up are presented. Methods: Cohort B enrolled pts who did not respond to or were intolerant to ≥4 weeks of abi or enza in the prechemotherapy mCRPC state and whose disease progressed within 6 months of screening (determined by PSA progression or radiologic bone/soft tissue progression). Pts received pembro 200 mg IV every 3 weeks (Q3W), docetaxel 75 mg/m2 IV Q3W, and oral prednisone 5 mg twice daily. Primary end points were safety, PSA response rate (PSA decrease >50% from baseline), and ORR per RECIST v1.1 by blinded independent central review. Efficacy and safety were assessed in all pts as treated. Results: Of the 104 treated pts, median age was 68.0 years (range, 50-86), 23.1% had PD-L1–positive tumors (combined positive score ≥1), 25.0% had visceral disease, and 50.0% had measurable disease. Median time from enrollment to data cutoff was 32.4 months (range 13.9-40.3); 101 pts discontinued, primarily because of disease progression (77.9%). Efficacy outcomes are reported in the table below. Treatment-related adverse events (TRAEs) occurred in 100 pts (96.2%); the most frequent (≥30%) were diarrhea (41.3%), fatigue (41.3%), and alopecia (40.4%). Grade 3-5 TRAEs occurred in 46 pts (44.2%). Five pts (4.8%) died of AEs; 2 were treatment-related pneumonitis. Conclusions: After another year of follow-up, pembro + docetaxel and prednisone showed improved ORR and PSA response rates compared to the prior dataset in pts with mCRPC previously treated with abi or enza. Safety was consistent with known profiles of each agent and will be further evaluated in a phase 3 study (KEYNOTE-921). Clinical trial information: NCT02861573. [Table: see text]

Pembrolizumab (pembro) plus olaparib in patients (pts) with docetaxel-pretreated metastatic castration-resistant prostate cancer (mCRPC): KEYNOTE-365 cohort A efficacy, safety, and biomarker results

5544

Background: Pembro + olaparib has shown antitumor activity and acceptable safety in docetaxel-pretreated pts with mCRPC enrolled in cohort A of the phase I/II KEYNOTE-365 study (NCT02861573). Updated results with new biomarker data are reported. Methods: Pts with docetaxel-pretreated mCRPC who progressed within 6 mo of screening received pembro 200 mg IV Q3W + olaparib 400-mg capsule or 300-mg tablet PO BID. Pts might have received 1 other chemotherapy and ≤2 second-generation androgen-receptor targeted therapies. Primary end points: PSA response rate (decrease ≥50% from baseline, confirmed by a second value ≥3 wks later), ORR per RECIST v1.1, and safety. Key secondary end points: DCR, DOR, rPFS, and OS. Biospecimens (eg, blood, tissue) were collected for biomarker analysis (tissue PD-L1 expression, androgen receptor variant 7 [AR-v7] expression in circulating tumor cells [CTCs], and a T-cell–inflamed gene expression profile [GEP]). ctDNA was analyzed by Guardant Health 360 (GH360) and Omni (GH Omni) assays. FFPE tissue was analyzed by FoundationOne CDx (F1CDx) assay. Results: 84 of 87 enrolled pts were treated; 48/84 (57.1%) had measurable disease. Median (range) time from enrollment to data cutoff was 3.6 mo (0.0-29.2) for all pts and 26.7 mo (21.2-29.2) for 41 pts with ≥27 wks’ follow-up. Confirmed PSA response rate was 9% (95% CI, 3.5-16.8) in 82 pts with a baseline PSA assessment. Median time to PSA progression: 3.8 mo (95% CI, 2.9-4.4). In 24 pts with measurable disease and ≥27 wks’ follow-up, ORR was 8.3% (95% CI, 1.0-27.0; 2 PRs) and DCR ≥6 mo was 20.8% (95% CI, 7.1-42.2). Median (range) DOR was NR (12.0+ to 21.4+ mo); 2 pts had DOR ≥12 mo. In all pts, median rPFS was 4.3 mo (95% CI, 3.4-7.7) and median OS was 14.4 mo (95% CI, 8.1-18.5). Grade ≥3 TRAEs occurred in 29 pts (35%); 2 pts died of TRAEs (1 myocardial infarction, 1 unknown). Overall, 26% had PD-L1+ tumors (combined positive score ≥1). Of 31 pts with CTC data, 12.9% were AR-v7+. No BRCA1/2 mutation was detected by GH360 (n=42). Of 57 pts analyzed by GH Omni, 2 had BRCA2 mutations, 1 had a BRCA1 mutation, 4 had ATM mutations, 1 had a CHEK1 mutation, and 6 had CDK12 mutations. Of 49 pts analyzed by F1CDx, 4 had BRCA mutations; 1 pt had a copy number loss mutation not detected by ctDNA analysis. GEP was not associated with ORR or PSA response. Conclusions: Pembro + olaparib continued to show activity and acceptable safety in pts with docetaxel-pretreated mCRPC. A phase III study of this combination is ongoing (KEYLYNK-010, NCT03834519). Clinical trial information: NCT02861573 .

Final overall survival (OS) from PROSPER: A phase III, randomized, double-blind, placebo (PBO)-controlled study of enzalutamide (ENZA) in men with nonmetastatic castration-resistant prostate cancer (nmCRPC)

5515

Background: PROSPER previously demonstrated a statistically significant and clinically meaningful improvement in metastasis-free survival (MFS) (hazard ratio [HR] 0.29; 95% CI 0.24-0.35; P < .001) in men with nmCRPC and rapidly rising prostate-specific antigen (PSA) who received ENZA. When first reported, OS was immature with only 165 of 596 (28%) prespecified deaths. Here we report results from the final OS analysis. Methods: Men with nmCRPC, PSA doubling time ≤ 10 mo, and PSA ≥ 2 ng/mL at screening continued androgen deprivation therapy (ADT) and were randomized 2:1 to ENZA 160 mg or PBO. OS treatment effect was assessed using a group sequential testing procedure with O’Brien-Fleming-type alpha spending function ( P ≤ .021 required for statistical significance). Medians were estimated using the Kaplan-Meier method; 95% CIs using a stratified Cox regression model. Results: As of Oct 15, 2019 (median follow-up ≈ 48 mo), there were 466 deaths (288 [30.9%] and 178 [38.0%] in the ENZA and PBO arms, respectively). ENZA significantly prolonged OS compared with PBO (HR 0.73; 95% CI 0.61-0.89; P = .0011). Median OS was 67.0 mo (95% CI 64.0-not reached) in the ENZA arm and 56.3 mo (95% CI 54.4-63.0) in the PBO arm. Subsequent antineoplastic therapies were initiated after treatment discontinuation by 310 (33%) men in the ENZA arm vs 303 (65%) in the PBO arm. Median duration of treatment was 33.9 mo vs 14.2 mo with ENZA vs PBO, respectively. Grade ≥ 3 adverse events (AEs) were reported by 48% of men in the ENZA arm vs 27% in the PBO arm (16% vs 6% were drug related, respectively). AEs with event rates per 100 patient-yr that were ≥ 2 points higher with ENZA vs PBO were falls (9 vs 4), fatigue (14 vs 12), and hypertension (7 vs 5). Conclusions: ENZA treatment resulted in a statistically significant 27% reduced risk of death compared with PBO, demonstrating that initiation of ENZA + ADT before the onset of detectable metastasis improves OS in men with CRPC and rapidly rising PSA. This OS benefit ensues despite crossover from the PBO arm to ENZA and higher rates of subsequent antineoplastic therapies in men from the PBO arm. Safety was consistent with previous clinical trials. This final OS analysis from PROSPER provides prospective validation of MFS as a potential surrogate endpoint for OS in nmCRPC and supports the continued use of ENZA + ADT as a standard of care in men with nmCRPC and rapidly rising PSA. Clinical trial information: NCT02003924 .

Prostate cancer biomarker enrichment and treatment selection (PC-BETS) study: A Canadian cancer trials group phase II umbrella trial for metastatic castration-resistant prostate cancer (mCRPC)

5551

Background: Genomic characterization of mCRPC has identified commonly occurring alterations but also recurrently mutated genes at much lower frequencies. To efficiently evaluate anti-tumor activity of novel targeted therapies in mCRPC patients (pts) we initiated an umbrella trial using circulating tumour DNA (ctDNA) to enrich accrual for cancers with alterations that may predict response. Methods: mCRPC pts that have progressed after treatment with a next generation AR-pathway inhibitor (ARPI) were enrolled to this multi-center, multi-arm, 2-stage phase II trial. Plasma cell-free DNA was subjected to targeted sequencing and pts allocated to a treatment arm by a Tumor Board (TB) based on a priori criteria (biomarker positive, BM+) or by randomization if biomarker negative (BM-). Primary objective was to determine the clinical benefit rate (CBR: PSA decline ≥50% (PSA50), CR/PR, or stable disease ≥12 weeks). We report on 1st-stage activity of arms evaluating inhibitors of CDK4/6 (palbociclib), WEE1 kinase (adavosertib), cMET (savolitinib) and the AR inhibitor darolutamide. Additional planned arms include inhibitors of AKT (ipatasertib), Polo-like Kinase 4 (CFI-400945), immune checkpoints (durvalumab, tremelimumab) and carboplatin. Results: 250 pts were screened from two sequential trials over 29 months at 11 centers. Median time from blood draw to TB decision was 35 days. 169 pts (68%) had detectable ctDNA (≥1%) with a mean ctDNA fraction of 24% (range 1-95%). Commonly detected genomic alterations involved AR (49% gain, 24% mutation), TP53 (49%), PTEN/PI3K pathway (35%), DNA repair (23%: mismatch repair (5%), BRCA2 (8%), ATM (3%), CDK12 (5%), other (2%)) and CTNNB1/APC (14%). To date, 46 BM+ pts and 37 BM- patients were enrolled: median age 70 years (53-88), 100% had prior ARPI, 45% had prior docetaxel, 17% with visceral metastases. Accrual and CBR are presented in table. Adverse events were as expected. Conclusions: Prospective centralized screening of ctDNA to stratify mCRPC pts into a precision oncology trial is feasible. Activity was seen in 4 of 7 evaluable cohorts with darolutamide and adavosertib, meeting the threshold for expansion of these arms. Clinical trial information: NCT03385655, NCT02905318 . [Table: see text]

Pembrolizumab (pembro) plus docetaxel and prednisone in patients (pts) with abiraterone acetate (abi) or enzalutamide (enza)-pretreated metastatic castration-resistant prostate cancer (mCRPC): KEYNOTE-365 cohort B efficacy, safety and, biomarker results

5550

Background: Pembro + docetaxel and prednisone (cohort B) has shown antitumor activity in pts with mCRPC in the phase I/II KEYNOTE-365 study (NCT02861573). Updated efficacy and safety and new biomarker data from cohort B are reported. Methods: Pts who received at least 4 wk of abi or enza in the prechemotherapy mCRPC setting and whose disease progressed within 6 mo of screening were eligible. Pts received pembro 200 mg IV + docetaxel 75 mg/m2 IV Q3W and prednisone 5 mg orally twice daily. Primary end points were PSA response rate (PSA decrease ≥50%; confirmed by a second value ≥3 weeks later), ORR per RECIST v1.1 by blinded independent central review, and safety. Key secondary end points were DCR per RECIST v1.1 (CR+PR+SD or non-CR/non-PD ≥6 mo), DOR per RECIST v1.1, radiographic PFS (rPFS) per PCWG-modified RECIST, and OS. Biospecimens (blood, tissue) were collected for biomarker analysis, including tissue PD-L1 expression, androgen receptor variant 7 (AR-v7) expression in circulating tumor cells, and a T-cell-inflamed gene expression profile (GEP). Results: Of 105 enrolled pts, 104 were treated, and 50% had measurable disease. Median (range) time from enrollment to data cutoff was 19.9 mo (1.4-27.8) for all pts and 21.8 mo (17.9-27.8) for pts with ≥27 wks follow-up (n=72). Confirmed PSA response rate was 28% in 103 pts with a baseline PSA assessment. Median time to PSA progression was 6.2 mo (95% CI, 3.7-7.4). In pts with measurable disease and ≥27 wks follow-up (n=39), ORR was 18% (7/39, all PRs) and DCR was 51%. Median DOR was 6.7 mo (range, 3.4-9.0+ [+ indicates ongoing responder]); 5 pts had a response for ≥6 mo. In all pts, median rPFS was 8.3 mo (95% CI, 7.6-10.1) and OS was 20.4 mo (16.9-NR). At 6 mo, the rPFS rate was 72.8% and OS rate was 95.3%. Treatment-related AEs (TRAEs) occurred in 96% of all pts; most frequent were alopecia (39%), diarrhea (38%), and fatigue (38%). Grade 3-5 TRAEs occurred in 40% of pts; 2 pts died of TRAEs (pneumonitis). Overall, 24% of pts were PD-L1+ (combined positive score ≥1). Of 57 pts with AR-v7 data, 17.5% were AR-v7+, 77% were AR-v7−, and 5% were undetermined. GEP was not significantly associated with ORR or PSA response. Conclusions: Pembro + docetaxel and prednisone showed activity in pts with abi or enza-pretreated mCRPC. Safety of the combination was consistent with the known profiles of the individual agents. A phase 3 study of this combination is ongoing (KEYNOTE-921, NCT03834506). Clinical trial information: NCT02861573 .

A phase I dose-escalation study of enzalutamide in combination with the AKT inhibitor AZD5363 (capivasertib) in patients with metastatic castration-resistant prostate cancer

BACKGROUND

Activation of the PI3K/AKT/mTOR pathway through loss of phosphatase and tensin homolog (PTEN) occurs in approximately 50% of patients with metastatic castration-resistant prostate cancer (mCRPC). Recent evidence suggests that combined inhibition of the androgen receptor (AR) and AKT may be beneficial in mCRPC with PTEN loss.

PATIENTS AND METHODS

mCRPC patients who previously failed abiraterone and/or enzalutamide, received escalating doses of AZD5363 (capivasertib) starting at 320 mg twice daily (b.i.d.) given 4 days on and 3 days off, in combination with enzalutamide 160 mg daily. The co-primary endpoints were safety/tolerability and determining the maximum tolerated dose and recommended phase II dose; pharmacokinetics, antitumour activity, and exploratory biomarker analysis were also evaluated.

RESULTS

Sixteen patients were enrolled, 15 received study treatment and 13 were assessable for dose-limiting toxicities (DLTs). Patients were treated at 320, 400, and 480 mg b.i.d. dose levels of capivasertib. The recommended phase II dose identified for capivasertib was 400 mg b.i.d. with 1/6 patients experiencing a DLT (maculopapular rash) at this level. The most common grade ≥3 adverse events were hyperglycemia (26.7%) and rash (20%). Concomitant administration of enzalutamide significantly decreased plasma exposure of capivasertib, though this did not appear to impact pharmacodynamics. Three patients met the criteria for response (defined as prostate-specific antigen decline ≥50%, circulating tumour cell conversion, and/or radiological response). Responses were seen in patients with PTEN loss or activating mutations in AKT, low or absent AR-V7 expression, as well as those with an increase in phosphorylated extracellular signal-regulated kinase (pERK) in post-exposure samples.

CONCLUSIONS

The combination of capivasertib and enzalutamide is tolerable and has antitumour activity, with all responding patients harbouring aberrations in the PI3K/AKT/mTOR pathway.

CLINICAL TRIAL NUMBER

NCT02525068.

KEYNOTE-365 cohort A updated results: Pembrolizumab (pembro) plus olaparib in docetaxel-pretreated patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

100

Background: KEYNOTE-365 (NCT02861573) is a phase 1b/2 study evaluating pembro + other agents in mCRPC. Updated results from cohort A (pembro + olaparib) are reported. Methods: Docetaxel-pretreated, molecularly unselected pts with mCRPC with progression within 6 mo of screening per PSA or radiologic bone/soft tissue progression enrolled. Pts may have received 1 other chemotherapy and ≤2 2nd-generation hormone therapy (HT). Pts received pembro 200 mg IV Q3W + olaparib 400 mg PO BID. Primary end points: safety, PSA response rate (confirmed PSA decline ≥50%), and ORR per blinded independent central review. Results: Of 84 treated pts, 42 discontinued, primarily due to progression (n=29). Median age was 71 y (range, 47-83); 26% were PD-L1+, 26% had visceral disease, and 57% had RECIST-measurable disease. Median follow-up was 3 mo for all pts (n=81) and 14 mo for pts with ≥27 wks’ follow-up (n=41). See Table for efficacy outcomes. Treatment-related AEs occurred in 70 (83%) pts. Most frequent (≥30%) were nausea (33%) and anemia (31%). Grade 3-5 treatment-related AEs occurred in 29 (35%) pts. Three pts died of AEs (2 treatment related [l myocardial infarction, 1 unknown cause]). Conclusions: With additional follow-up, pembro + olaparib continued to show activity in docetaxel-pretreated, molecularly unselected pts who previously received HT for mCRPC. Safety of the combination was consistent with individual profiles of each agent. Clinical trial information: NCT02861573. [Table: see text]

PROfound: Efficacy of olaparib (ola) by prior taxane use in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and homologous recombination repair (HRR) gene alterations

134

Background: Optimal sequencing of therapies for mCRPC is not established. In the Phase III PROfound study (NCT02987543), ola significantly prolonged radiographic progression-free survival (rPFS) vs physician’s choice of new hormonal agent (pcNHA) in pts with mCRPC and an alteration in genes with a direct or indirect role in HRR. We report exploratory subgroup analyses by prior taxane (yes vs no). Methods: Men with mCRPC that had progressed on prior NHA were randomized to ola (tablets; 300 mg bid) or pcNHA (enzalutamide or abiraterone). Pts had alterations in BRCA1, BRCA2 or ATM (Cohort A) or ≥1 of 12 other prespecified genes with a direct or indirect role in HRR (Cohort B). Stratification factors were prior taxane use and measurable disease. rPFS was assessed by blinded independent central review with RECIST v1.1 + PCWG3. Results: Subgroup analyses of rPFS and overall survival (OS) favored ola vs pcNHA irrespective of prior taxane in Cohort A, Cohorts A+B and pts with a BRCA1 and/or BRCA2 or CDK12 alteration (Table). In the ATM subgroup hazard ratio (HR) point estimates for rPFS and OS were lower in pts who had received prior taxane vs pts who had not, but 95% CIs overlapped and pt numbers were small so data should be interpreted with caution. Conclusions: The benefit of ola over pcNHA in pts with mCRPC and HRR gene alterations was generally independent of prior taxane status in the overall study population. Clinical trial information: NCT02987543. [Table: see text]

Real-world management of advanced prostate cancer: A Canadian comparison of academic specialists and community-based prostate cancer physicians

29

Background: The Canadian GU Research Consortium recently conducted a consensus development conference with 27 academic prostate cancer (PC) specialists leading to 31 consensus recommendations. We conducted a survey to compare community-based practice with the consensus recommendations on the management of metastatic castration sensitive prostate cancer (mCSPC), metastatic castration resistant prostate cancer (mCRPC) and non-metastatic castration resistant prostate cancer (nmCRPC). Methods: An 87-item online questionnaire was sent to 600 Canadian community urologists, medical oncologists, radiation oncologists, and general practitioner oncologists involved in the treatment of PC. Results: Seventy-two physicians responded to the questionnaire (12% response). A discordance of >25% was observed in 15 of 31 recommendations (48%). Among the areas of discordance were treatment approach for patients with nmCRPC and PSADT < 10 months who are negative for metastases on conventional imaging but metastatic on PET-based imaging. Of the academic physicians, 89% indicated treating with agents approved for nmCRPC compared to 50% of community physicians (p=0.0005). Important discrepancies were also observed across academic and community physicians for radiation to the prostate for low-volume mCSPC which was 74% vs 27%, (p<0.0001) respectively; criteria for stopping therapy in mCRPC in which 78% of academic physicians favored continuation of therapy in the event of PSA progression only, compared to 24% of community physicians. Sequencing of therapy after prior apalutamide for nmCRPC using subsequent docetaxel treatment was observed in 81% of academic physicians vs 35% of community physicians, (p<0.0001), and use of genetic testing was favored by 74% of academics vs 36% of community physicians, (p<0.0001) for newly diagnosed metastatic prostate cancer. Conclusions: The areas of discordance between a national sample of community-based PC physicians and academic consensus recommendations represent potential areas for education, practice tools and future research.

Edmonton Prostate Interdisciplinary Cancer Clinic (EPICC): Real-world efficacy outcomes of a multidisciplinary clinic for metastatic castration-resistant prostate cancer

36

Background: Multidisciplinary management improves complex treatment decision making in cancer care but its impact for metastatic castration resistant prostate cancer (M1 CRPC) has not been documented. The Edmonton Prostate Interdisciplinary Cancer Clinic (EPICC) is a multidisciplinary specialized clinic focused on the delivery of novel therapeutics (Androgen Receptor Axis Therapy; ARAT) to men with chemotherapy-naïve M1 CRPC. The objective of the current study was to assess the efficacy of ARAT in the EPICC. Methods: The study was a retrospective quality assurance analysis. Eligible patients had a new diagnosis of chemotherapy-naïve M1 CRPC with minimal symptoms. EPICC patients were assessed and treated by a multidisciplinary cancer control team that included nursing oncology, pharmacy oncology and physician oncology (urologic, medical and radiation). Patients were treated in first line with an ARAT (abiraterone (AA) or enzalutamide (EZ)) from October 2017 to March 2018. The main efficacy outcome was overall survival (OS). The Kaplan-Meier method and Cox regression model were used to analyze survival data. Statistical tests were two-sided (p≤0.05). Results: From October 2017 to March 2018, 160 chemotherapy-naïve M1 CRPC patients were assessed in the EPICC. Median age at EPICC admission was 77 years (range, 54-92 years). Median PSA level at EPICC admission was 26.6 ng/mL (range, 0.1-5000 ng/mL). 84 out of 160 (53%) patients had received prior radical local therapy (RLT) with curative intent. 83 (57%) patients were treated with EZ and 64 (43%) patients were treated AA. Median OS for the entire cohort was 23 months. In multivariable analysis, absence of prior RLT (HR 3.6, 95% CI 1.9 to 6.6, p < 0.001), PSA > 20 ng/mL (HR 3.2, 95% CI 1.4 to 7.2, p = 0.004), and higher ECOG performance status (1 vs 0: HR 2.4, 95% CI 1.3 to 4.4, p = 0.005; 2 versus 0: HR 3.5, 95% CI 1.5 to 8.0, p = 0.003; and 3 versus 0: HR 12.7, 95% CI 2.5 to 63.8, p = 0.002) were independently associated with poorer OS. Conclusions: Multidisciplinary management of chemotherapy-naïve M1 CRPC with ARAT is feasible. Real world efficacy of ARAT in EPICC are similar to data reported in phase 3 trials.

KEYNOTE-365 cohort B updated results: Pembrolizumab (pembro) plus docetaxel and prednisone in abiraterone (abi) or enzalutamide (enza)-pretreated patients (pts) with metastatic castrate-resistant prostate cancer (mCRPC)

103

Background: KEYNOTE-365 (NCT02861573) is a phase 1b/2 study to evaluate pembro in combination with other agents in mCRPC. Here we report updated results from cohort B (pembro + docetaxel and prednisone). Methods: Cohort B enrolled pts who failed or were intolerant to ≥4 wk of abi or enza in the prechemotherapy mCRPC state and whose disease progressed within 6 mo of screening as determined by PSA progression or radiologic bone/soft tissue progression. Pts received pembro 200 mg IV + docetaxel 75 mg/m2 IV Q3W and prednisone 5 mg orally twice daily. Primary end points were safety, PSA response rate (confirmed PSA decrease >50%), and ORR per blinded independent central review (BICR). Results: Of 104 treated pts, 72 discontinued, primarily due to progression (55%). Median age was 68 y (range 50-86), 24% were PD-L1+, 25% had visceral disease, and 50% had measurable disease. Median follow-up was 13 mo for all pts (n=104) and 19 mo for pts who had ≥27 wk of follow up (n=72). See table for efficacy outcomes. Treatment-related AEs occurred in 100 pts (96%); most frequent (≥30%) were alopecia, diarrhea, and fatigue (39% each). Grade 3-5 treatment-related AEs occurred in 42 pts (40%). Five pts died of AEs; 2 deaths were from treatment-related AEs (pneumonitis). Conclusions: With additional follow-up, pembro + docetaxel and prednisone continued to show activity in pts with mCRPC who failed previous antihormonal therapy. Safety of the combination was consistent with the known profiles of the individual agents and will be further evaluated in a phase 3 study (KEYNOTE-921). Clinical trial information: NCT02861573. [Table: see text]

High-dose chemotherapy with autologous stem cell transplantation (HDC-ASCT) for relapsed metastatic germ cell tumors (mGCTs): The Alberta experience from 2001 to 2018

406

Background: HDC-ASCT is a standard therapy for patients (pts) with mGCTs whose disease progresses on or after conventional dose chemotherapy. We conducted a retrospective review of HDC-ASCT in pts with relapsed mCGT in Alberta over the past two decades. Methods: Pts with mGCTs who received HDC-ASCT at two provincial referral cancer centers in Alberta, Canada from 2001-2018 were identified. Baseline clinical and treatment characteristics were collected as well as overall survival (OS) and disease-free survival (DFS). Relevant prognostic variables were analyzed. Results: Forty three pts were identified. Median age was 28 years (range 19 – 56). Majority (95%) had non-seminoma histology and testis/retroperitoneal primary (84%). Twenty pts (47%) had poor risk disease as per IGCCC at start of first-line chemotherapy. HDC-ASCT was used as second-line therapy in 65% and 58% received tandem HDC-ASCT. Median follow-up from ASCT was 22 months (range 2 – 181). At last follow-up, 42% of pts are alive without disease, including 3/7 (43%) of pts with primary mediastinal disease. Two-year and 5-year DFS/OS were 44%/51% and 41%/43%, respectively. Median OS and DFS for all pts were 27.9 months (10.2 – NR) and 9.3 months (4.2 – 124), respectively. Conclusions: We found that HDC-ASCT is an effective salvage therapy in mGCT, consistent with existing literature. Pts appeared to benefit regardless of primary site. Though limited by small sample size, we found a numerical difference in DFS and OS between 2nd and 3rd line HDC-ASCT and single vs. tandem ASCT.[Table: see text]

Genetic Analysis of Circulating Tumour Cells

The classification of human cancers has traditionally relied on the tissue of origin, the histologic appearance and anatomical extent of disease, otherwise referred to as grade and stage. However, this system fails to explain the highly variable clinical behaviour seen for any one cancer. Molecular characterization through techniques such as next-generation sequencing (NGS) has led to an appreciation of the extreme genetic heterogeneity that underlies most human cancers. Because of the difficulties associated with fresh tissue biopsy, interest has increased in using circulating tumour material, such as circulating tumour cells (CTCs), as a non-invasive way to access tumour tissue. CTC enumeration has been demonstrated to have prognostic value in metastatic breast, colon and prostate cancers. Recent studies have also shown that CTCs are suitable material for molecular characterization, using techniques such as reverse transcription-polymerase chain reaction (RT-PCR), fluorescence in situ hybridization (FISH), array comparative genomic hybridization (aCGH) and NGS. Furthermore, genetic analysis of CTCs may be more suitable to study tumour heterogeneity and clonal evolution than fresh tissue biopsy. Whether blood-based biopsy techniques will be accepted as a replacement to fresh tissue biopsies remains to be seen, but there is reason for optimism. While significant barriers to this acceptance exist, blood-based biopsy techniques appear to be reliable and representative alternatives to fresh tissue biopsy.

Pembrolizumab (pembro) plus docetaxel and prednisone in abiraterone (abi) or enzalutamide (enza)-pretreated patients (pts) with metastatic castrate resistant prostate cancer (mCRPC): Cohort B of the phase 1b/2 KEYNOTE-365 study

5029

Background: Pembro had activity as monotherapy in pretreated advanced mCRPC. Data are presented here from cohort B (pembro + docetaxel/prednisone) of KEYNOTE-365 (NCT02861573), a phase 1b/2 umbrella study to test combinations in mCRPC. Methods: Pts who progressed on or became intolerant to ≥4 wk of abi or enza in the prechemotherapy mCRPC state and progressed within 6 mo before screening were eligible. Pts received pembro 200 mg IV with docetaxel 75 mg/m2 IV Q3W plus prednisone 5 mg orally twice daily. The primary end points were safety and PSA response rate (confirmed PSA decrease ≥50%). Key secondary end points were investigator-determined ORR (RECIST v1.1), disease control rate (DCR: CR+PR+SD ≥6 mo), time to PSA progression, rPFS, and OS. Results: 72 pts (median age, 68 y; visceral disease, 36%; measurable disease, 50%) began pembro + docetaxel. Median (95% CI) follow-up was 10 (8-12) mo. Efficacy is outlined in the table. Treatment-related AEs occurred in 69 (96%) pts; most frequent (≥30%) were alopecia (43%), fatigue (40%), and diarrhea (39%). Grade 3-5 treatment-related AEs occurred in 27 (38%) pts, including 2 deaths from treatment-related AEs (pneumonitis). Most commonly reported immune-mediated AEs were infusion-related reactions (11%) and colitis (10%). Conclusions: Pembro + docetaxel/prednisone has activity in pts with mCRPC who previously progressed on second-generation hormone therapy. AEs were considered mild for the treatment combination. Clinical trial information: NCT02861573. [Table: see text]

Centralization of radical cystectomy for bladder cancer in a universal healthcare system: Early results from a Canadian academic center

516

Background: Radical cystectomy for bladder cancer is a complex surgical oncology procedure. Centralization of this procedure to high volume, fellowship-trained surgeons may improve clinical outcomes. Our objective was to compare outcomes of radical cystectomy before and after centralization of care. Methods: A retrospective analysis of data from the University of Alberta Radical Cystectomy Database was performed. Eligible subjects were those with histologically proven urothelial carcinoma of the bladder (cTanyN1-3M0) undergoing curative intent surgery. Patients were classified into pre-centralization era (1994-2007; N = 523) and post-centralization era (2013-present; N = 134) cohorts for analyses. Pre-centralization era patients were treated by 1 of 11 urologic surgeons at 2 academic teaching hospitals. Post-centralization era patients were treated by 1 of 2 fellowship-trained urologic oncologists at 1 academic teaching hospital. Outcomes were overall survival, 90-day mortality rate, positive surgical margin (R1) resection rate, total number of lymph nodes evaluated, and 90-day blood product transfusion rate. The Kaplan-Meier method and multivariable regression analyses were used to analyze survival outcomes. Statistical tests were two-sided (p≤0.05). Results: The median follow-up duration in the pre- and post-centralization era was 33 months and 16 months, respectively. The predicted 2-year overall survival rate was 62% in the pre-centralization era and 84% in the post-centralization era (Log rank P = 0.0007; multivariable HR 0.40, 95% CI 0.24 to 0.68, P < 0.0001). Treatment in the post-centralization era was associated with lower 90-day mortality (6.3% versus 1.5%, multivariable OR 0.23, 95% CI 0.06 to 0.99, P = 0.049), R1 resection (13.0% versus 1.5%; multivariable OR 0.07, 95% CI 0.01 to 0.51, P = 0.009), and 90-day blood product transfusion (59% versus 6%, P < 0.0001) as well as higher total number of lymph nodes evaluated (7 versus 30 lymph nodes, P < 0.0001). Conclusions: Surgical treatment in the post-centralization era was associated with superior survival, cancer control, and perioperative outcomes.

Clinical outcome of patients with germline DNA repair mutations: Results from a retrospective international study

218

Background: CRPC is enriched for germline mutations in DNA damage repair genes (gDDRm). BRCA2 mutations (g BRCA2m) associate with poor prognosis from localized PC, but prognostic and predictive value for standard therapy in CRPC is unclear. We reviewed clinical outcome of 390 patients previously tested for gDDRm. Methods: Patient records were reviewed for 372 patients from 3 institutions (Royal Marsden UK, Weill-Cornell NY, University of Washington, WA) with gDDRm status previously published (Pritchard et al, NEJM 2016) and 18 g BRCA1/2m carriers from KConFab consortium (Australia). Baseline characteristics and survival were annotated. Response (PSA50%/RECIST) and PFS (RECIST/PSA progression or start of a new therapy due to clinical progression) were collected for Abiraterone, Enzalutamide and Docetaxel. To account for potential differences between cohorts, a mixed effect model (Weibull distribution) with random intercept per cohort was pursued. Results: dDDRm status was available for n = 390 (60 gDDRm+, including 37 g BRCA2m, and 330 gDDRm-). Overall, 74% and 69% received Docetaxel and Abiraterone/Enzalutamide respectively; 47% gDDRm+ and 34% gDDRm- received PARPi and/or platinum. Median overall survival from CRPC was 3.0 vs 3.2 years in gDDRm+ vs gDDRm- (p = 0.73; g BRCA2m = 3.0 years, p = 0.72). Age and Gleason score at diagnosis were associated with survival from castration-resistance in multivariate analysis. Median PFS on Docetaxel for gDDRm+ (6.8 months; 6.3 for g BRCA2m) and gDDRm- (5.1 months) were not significantly different (p = 0.2). Similarly, RR to Docetaxel was similar for the two groups (61% vs 54% in gDDRm+ vs gDDRm-; 63% g BRCA2m). Median PFS and RR on first Abiraterone/Enzalutamide were similar across groups (PFS: 8.3 months gDDRm+, 8.3 months for gDDRm-; p = 0.9; RR 46% vs 56% respectively) The Interaction of PARPi/platinum therapy among gDDRm+ patients resulted in an aHR for OS from CRPC of 0.59 (95%CI 0.28-1.25; p = 0.17). Conclusions: In this retrospective analysis, CRPC patients with gDDRm still benefited from standard therapies similarly to non-mutation carriers; interpretation of survival data should consider the high proportion treated with PARPi/platinum.

A phase I dose-escalation study of enzalutamide in combination with the AKT inhibitor AZD5363 in patients with mCRPC

135

Background: Activation of the PI3K/AKT/mTOR pathway may contribute to resistance to androgen receptor targeted therapies in metastatic CRPC (mCRPC). The phase I/II RE-AKT trial (NCT02525068) investigates the safety and activity of enzalutamide (enza) in combination with the AKT inhibitor, AZD5363, in patients (pts) with mCRPC. Results of the phase I run-in are reported. Methods: mCRPC pts progressing after 1-2 lines of taxane chemotherapy and at least 12 weeks (wks) of abiraterone or enza were treated with enza (160mg od) and AZD5363 bid 4-days on, 3-days off, in a 3+3 dose escalation design. Co-primary endpoints were to assess toxicity (CTCAE), and identify the recommended phase II dose (RP2D) of AZD5363; antitumour activity and pharmacokinetics (PK) were secondary endpoints. Response was assessed by PSA, RECIST v1.1 and circulating tumor cell (CTC) conversion. Pts were considered evaluable for response if they completed 12 wks of treatment. Results: 16 pts were enrolled between 12/2014 & 04/2016 with 15 receiving treatment. At the AZD5363 320mg dose 3 pts were treated with no dose limiting toxicity (DLT). At the AZD5363 480mg dose, 5 pts were treated with 2 DLTs of grade (G) 3 maculopapular rash (MPR) related to AZD5363. An intermediate dose level of AZD5363 400mg was selected with 7 pts treated. 1 pt withdrew consent prior to completing the DLT window. 1 DLT of G3 MPR occurred and this dose was selected as the RP2D. Non-DLT treatment related (TR) G3/4 adverse events (AEs) were hyperglycaemia (n = 4, 26.7%), neutropenia (n = 1, 6.7%) & diarrhea (n = 1, 6.7%). All other TR AEs were G1 or G2, with diarrhea (n = 9, 60%), anorexia (n = 8, 53.3%) & nausea (n = 7, 46.7%) being most common. Of the 10 pts who completed 12 wks of treatment, 3 met at least one of the criteria for response. 1 pt (AZD5363 320mg) who had previously progressed on enza exhibited RECIST v1.1 partial response, > 50% PSA response, and CTC conversion by wk 13. Enza decreased AZD5363 PK exposure; robust modulation of pS6, pGSK3b and pPRAS40 was demonstrated. Conclusions: AZD5363 at the RP2D of 400mg bid 4 days on, 3 days off combined with enza 160mg od is safe and tolerable. Antitumor activity is reported, suggesting that AZD5363 may be able to overcome resistance to enza. Clinical trial information: NCT02525068.

Loco-regional treatment (LRT) for M1 at diagnosis prostate cancer (PCa) patients (pts) and impact on overall survival (OS): A retrospective analysis

280

Background: The optimal management of the primary tumour in pts with M1 at diagnosis PCa is not established. We aimed to evaluate the impact on OS of LRT (surgery or radiotherapy to the primary tumour) in de novo metastatic disease. Methods: PCa pts with M1 disease at diagnosis treated at the Royal Marsden between June 2003 and December 2011 were evaluated. LRT+ patients were defined as those that had received surgery or radiotherapy for the primary. Covariates analysed included age, diagnostic Gleason score, lines of CRPC treatment, PSA, burden of bone metastases ( ≥ 4 vs < 4 bone metastases) and ECOG PS. Kaplan-Meier analyses generated OS data. The association between LRT and OS was evaluated in univariate (UV) and multivariate (MV) Cox regression models. Results: Overall 234 pts with M1 at diagnosis were identified; 27 (11.53%) received LRT (25 XRT; 2 prostatectomy). Median time interval between diagnosis and LRT was 782 days (range 0-4130). Patients receiving LRT were younger (49 vs 61 yrs, p = 0.042), had lower baseline PSA values (68 vs 148; p < 0.001), and were more likely to have lymph node only disease (26% vs 10%; p = 0.029) and a lower burden of bone metastases with < 4 metastases (85% vs 34%;p < 0.001). Patients receiving LRT had a significantly longer survival (74.2 vs 55.1 months; HR 0.39; p < 0.001) in UV and MV cox-regression analysis (table). LRT+ remained highly prognostic, independently of disease volume at diagnosis and baseline PSA. Conclusions: LRT was associated with increased survival in patients with de novo metastatic disease, and in these analyses the prognostic utility of this LRT prognostic biomarker was independent of volume of metastatic disease at baseline and I'd baseline PSA. Other possible confounder factors may need to be taken into account when interpreting these results which require prospective validation from clinical trials such as STAMPEDE . [Table: see text]

Association between PSA declines at 4 weeks and OS in patients treated with abiraterone acetate (AA) for metastatic castration resistant prostate cancer (mCRPC) after docetaxel

215

Background: Falls in prostate specific antigen (PSA) levels by 50% from the baseline at 12 weeks are currently used to assess response to treatment for mCRPC (Scher et al, 2008). However PSA decline algorithms do not provide robust intermediate endpoints of overall survival (OS) benefit in mCRPC. We evaluated the association between PSA decline at 4 weeks and OS. Methods: We identified mCRPC patients who had received treatment with abiraterone acetate (AA) plus prednisolone post-docetaxel at the Royal Marsden (London, UK) between 01.01.2006 and 30.04.14. Patients were eligible for this analysis if they had PSA levels assessed at baseline, after 4 weeks and 12 weeks of treatment. PSA response at 4 weeks was defined as a ≥30% (PSA4w30) and ≥50% (PSA4w50) decline from baseline (PSABL). Association with outcome was analyzed using multivariate Cox regression and log-rank analyses. A significant p-value of 0.0167 was pre-specified to account for multiple testing. Demographics and clinical data were retrospectively collected from the hospital electronic patient record system (EPR). Results: We identified 124 patients who had received AA post-docetaxel and were eligible for this analysis. PSA4w30 was associated with longer OS (median OS 11.1 vs. 6.8 months; HR 0.50; 95% CI 0.32-0.80; p=.004). PSA4w50 was not associated with OS. A ≥50% PSA decline at 12 weeks (PSA12w50), the standard response measure, was also associated with OS (median OS 9.3 vs. 8.2; HR 0.49; 95% CI 0.29-0.80; p=.005). PSA4w30 was significantly associated with PSA12w50 (p<.001). Lack of a PSA response at 4 weeks correlated with a lack of response at 12 weeks (p=0.000), with a sensitivity of 84.9% [95% CI 75-91.4] and a specificity of 86.5% [95%CI 72–94.1]). PSA4w30 remained significantly correlated with OS (P<.001) in multivariate analyses including other established prognostic factors in mCRPC (ECOG PS, albumin, PSABL, ALP, LDH, Hemoglobin). Conclusions: Further studies to identify mCRPC patients not responding to treatment as early as possible are warranted; PSA4w30 may be useful to help identify patients unlikely to benefit from AA.