Diagnosis and management of neuroendocrine prostate cancer.

BACKGROUND: Although most patients with prostate cancer (PC) respond to initial androgen deprivation therapy (ADT), castration-resistant disease invariably develops. Progression to treatment-emergent neuroendocrine PC (t-NEPC) represents a unique mechanism of resistance to androgen receptor (AR)-targeted therapy in which lineage plasticity and neuroendocrine differentiation induce a phenotypic switch from an AR-driven adenocarcinoma to an AR-independent NEPC. t-NEPC is characterized by an aggressive clinical course, increased resistance to AR-targeted therapies, and a poor overall prognosis. METHODS: This review provides an overview of our current knowledge of NEPC, with a focus on the unmet needs, diagnosis, and clinical management of t-NEPC. RESULTS: Evidence extrapolated from the literature on small cell lung cancer or data from metastatic castration-resistant PC (mCRPC) cohorts enriched for t-NEPC suggests an increased sensitivity to platinum-based chemotherapy. However, optimal strategies for managing t-NEPC have not been established, and prospective clinical trial data are limited. Intertumoral heterogeneity within a given patient, as well as the lack of robust molecular or clinical biomarkers for early detection, often lead to delays in diagnosis and prolonged treatment with suboptimal strategies (i.e., conventional chemohormonal therapies for mCRPC), which may further contribute to poor outcomes. CONCLUSIONS: Recent advances in genomic and molecular classification of NEPC and the development of novel biomarkers may facilitate an early diagnosis, help to identify promising therapeutic targets, and improve the selection of patients most likely to benefit from NEPC-targeted therapies.

Pembrolizumab plus Abiraterone Acetate and Prednisone in Patients with Chemotherapy-naïve Metastatic Castration-resistant Prostate Cancer: Results from KEYNOTE-365 Cohort D.

BACKGROUND AND OBJECTIVE: Abiraterone acetate (abiraterone) plus prednisone is approved for the treatment of metastatic castration-resistant prostate cancer (mCRPC). Our aim was to evaluate the efficacy and safety of pembrolizumab plus abiraterone in mCRPC. METHODS: In cohort D of the phase 1b/2 KEYNOTE-365 study (NCT02861573), patients were chemotherapy-naïve, had disease progression ≤6 mo before screening, and had either not received prior next-generation hormonal agents for mCRPC or had received prior enzalutamide for mCRPC and had disease progression or became intolerant to enzalutamide. Patients received pembrolizumab 200 mg intravenously every 3 wk plus abiraterone 1000 mg orally once daily and prednisone 5 mg orally twice daily. The primary endpoints were safety, prostate-specific antigen (PSA) response rate, and objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) by blinded independent central review (BICR). Secondary endpoints included radiographic progression-free survival (rPFS) according to Prostate Cancer Clinical Trials Working Group 3-modified RECIST v1.1 by BICR and overall survival (OS). KEY FINDINGS AND LIMITATIONS: For the 103 patients who were treated, median follow-up was 28 mo (interquartile range 26-31). The confirmed PSA response rate was 56% (58/103 patients). The ORR for patients with RECIST v1.1-measurable disease was 16% (6/37 patients). Median rPFS was 15 mo (95% confidence interval 9.2-22) and median OS was 30 mo (95% confidence interval 23-not reached); the estimated 24-mo OS rate was 58%. In total, 91% of patients experienced treatment-related adverse events, and 39% experienced grade 3-5 events. Grade 3/4 elevation of alanine aminotransferase (ALT) or aspartate aminotransferase (AST) was observed in 12% and 6.8% of patients, respectively. One patient died due to treatment-related myasthenic syndrome. Study limitations include the single-arm design. CONCLUSIONS: Pembrolizumab plus abiraterone and prednisone demonstrated antitumor activity and acceptable safety in patients with chemotherapy-naïve mCRPC. Higher incidence of grade 3/4 elevated ALT/AST occurred than was reported for the individual agents. PATIENT SUMMARY: For patients with metastatic castratation-resistant prostate cancer, the drug combination of pembrolizumab plus abiraterone and prednisone showed antitumor activity and acceptable safety.

Pembrolizumab plus enzalutamide for metastatic castration-resistant prostate cancer progressing on enzalutamide: cohorts 4 and 5 of the phase 2 KEYNOTE-199 study.

BACKGROUND: KEYNOTE-199 (NCT02787005) is a multicohort phase 2 study evaluating pembrolizumab in patients with metastatic castration-resistant prostate cancer (mCRPC). Results from cohorts 4 (C4) and 5 (C5) are presented. METHODS: Eligible patients had not received chemotherapy for mCRPC and had responded to enzalutamide prior to developing resistance as defined by Prostate Cancer Clinical Trials Working Group 3 guidelines. Patients with RECIST-measurable disease were enrolled in C4, and patients with bone-only or bone-predominant disease were enrolled in C5. All patients received pembrolizumab 200 mg every 3 weeks for ≤35 cycles with ongoing enzalutamide until progression, unacceptable toxicity, or withdrawal. The primary end point was objective response rate (ORR) per RECIST v1.1 by blinded independent central review in C4. Secondary end points included disease control rate (DCR), overall survival, and safety in each cohort and both cohorts combined. RESULTS: A total of 126 patients were treated (C4, n = 81; C5, n = 45). Median age was 72 years (range 43-92), and 87.3% had received ≥6 months of enzalutamide prior to study entry. Confirmed ORR was 12.3% (95% CI 6.1-21.5%) for C4. Median duration of response in C4 was 8.1 months (range, 2.5+ to 15.2), and 5 of these patients experienced an objective response lasting ≥6 months. DCR was 53.1% (95% CI 41.7-64.3%) in C4 and 51.1% (95% CI 35.8-66.3%) in C5. Median overall survival was 17.6 months (95% CI 14.0-22.6) in C4 and 20.8 months (95% CI 14.1-28.9) in C5. Grade ≥3 treatment-related adverse events occurred in 35 patients (27.8%); 2 patients in C4 died from immune-related adverse events (myasthenic syndrome and Guillain-Barré syndrome). CONCLUSIONS: The addition of pembrolizumab to ongoing enzalutamide treatment in patients with mCRPC that progressed on enzalutamide after initial response demonstrated modest antitumor activity with a manageable safety profile. CLINICAL TRIAL REGISTRY AND ID: ClinicalTrials.gov, NCT02787005.