First-line combination treatment with PARP and androgen receptor-signaling inhibitors in HRR-deficient mCRPC: Applying clinical study findings to clinical practice in the United States.

INTRODUCTION: Metastatic castration-resistant prostate cancer (mCRPC) remains incurable and develops from biochemically recurrent PC treated with androgen deprivation therapy (ADT) following definitive therapy for localized PC, or from metastatic castration-sensitive PC (mCSPC). In the mCSPC setting, treatment intensification of ADT plus androgen receptor (AR)-signaling inhibitors (ARSIs), with or without chemotherapy, improves outcomes vs ADT alone. Despite multiple phase 3 trials demonstrating a survival benefit of treatment intensification in PC, there remains high use of ADT monotherapy in real-world clinical practice. Prior studies indicate that co-inhibition of AR and poly(ADP-ribose) polymerase (PARP) may result in enhanced benefit in treating tumors regardless of alterations in DNA damage response genes involved either directly or indirectly in homologous recombination repair (HRR). Three recent phase 3 studies evaluated the combination of a PARP inhibitor (PARPi) with an ARSI as first-line treatment for mCRPC: TALAPRO-2, talazoparib plus enzalutamide; PROpel, olaparib plus abiraterone acetate and prednisone (AAP); and MAGNITUDE, niraparib plus AAP. Results from these studies have led to the recent approval in the United States of talazoparib plus enzalutamide for the treatment of mCRPC with any HRR alteration, and of both olaparib and niraparib indicated in combination with AAP for the treatment of mCRPC with BRCA alterations. SUMMARY: Here, we review the newly approved PARPi plus ARSI treatments within the context of the mCRPC treatment landscape, provide an overview of practical considerations for the combinations in clinical practice, highlight the importance of HRR testing, and discuss the benefits of treatment intensification for patients with mCRPC.

First-line talazoparib with enzalutamide in HRR-deficient metastatic castration-resistant prostate cancer: the phase 3 TALAPRO-2 trial.

Preclinical evidence has suggested an interplay between the androgen receptor, which largely drives the growth of prostate cancer cells, and poly(ADP-ribose) polymerase. This association provides a rationale for their co-inhibition for the treatment of metastatic castration-resistant prostate cancer (mCRPC), an area of unmet medical need. The phase 3 TALAPRO-2 study investigated combining the poly(ADP-ribose) polymerase inhibitor talazoparib with enzalutamide versus enzalutamide alone as first-line treatment of mCRPC. Patients were prospectively assessed for tumor alterations in DNA damage response genes involved in homologous recombination repair (HRR). Two cohorts were enrolled sequentially: an all-comers cohort that was enrolled first (cohort 1; N = 805 (169 were HRR-deficient)), followed by an HRR-deficient-only cohort (cohort 2; N = 230). We present results from the alpha-controlled primary analysis for the combined HRR-deficient population (N = 399). Patients were randomized in a 1:1 ratio to talazoparib or placebo, plus enzalutamide. The primary endpoint, radiographic progression-free survival, was met (median not reached at the time of the analysis for the talazoparib group versus 13.8 months for the placebo group; hazard ratio, 0.45; 95% confidence interval, 0.33 to 0.61; P < 0.0001). Data for overall survival, a key secondary endpoint, are immature but favor talazoparib (hazard ratio, 0.69; 95% confidence interval, 0.46 to 1.03; P = 0.07). Common adverse events in the talazoparib group were anemia, fatigue and neutropenia. Combining talazoparib with enzalutamide significantly improved radiographic progression-free survival in patients with mCRPC harboring HRR gene alterations, supporting talazoparib plus enzalutamide as a potential first-line treatment for these patients. ClinicalTrials.gov Identifier: NCT03395197 .

Talazoparib plus enzalutamide in men with first-line metastatic castration-resistant prostate cancer (TALAPRO-2): a randomised, placebo-controlled, phase 3 trial.

BACKGROUND: Co-inhibition of poly(ADP-ribose) polymerase (PARP) and androgen receptor activity might result in antitumour efficacy irrespective of alterations in DNA damage repair genes involved in homologous recombination repair (HRR). We aimed to compare the efficacy and safety of talazoparib (a PARP inhibitor) plus enzalutamide (an androgen receptor blocker) versus enzalutamide alone in patients with metastatic castration-resistant prostate cancer (mCRPC). METHODS: TALAPRO-2 is a randomised, double-blind, phase 3 trial of talazoparib plus enzalutamide versus placebo plus enzalutamide as first-line therapy in men (age ≥18 years [≥20 years in Japan]) with asymptomatic or mildly symptomatic mCRPC receiving ongoing androgen deprivation therapy. Patients were enrolled from 223 hospitals, cancer centres, and medical centres in 26 countries in North America, Europe, Israel, South America, South Africa, and the Asia-Pacific region. Patients were prospectively assessed for HRR gene alterations in tumour tissue and randomly assigned (1:1) to talazoparib 0·5 mg or placebo, plus enzalutamide 160 mg, administered orally once daily. Randomisation was stratified by HRR gene alteration status (deficient vs non-deficient or unknown) and previous treatment with life-prolonging therapy (docetaxel or abiraterone, or both: yes vs no) in the castration-sensitive setting. The sponsor, patients, and investigators were masked to talazoparib or placebo, while enzalutamide was open-label. The primary endpoint was radiographic progression-free survival (rPFS) by blinded independent central review, evaluated in the intention-to-treat population. Safety was evaluated in all patients who received at least one dose of study drug. This study is registered with ClinicalTrials.gov (NCT03395197) and is ongoing. FINDINGS: Between Jan 7, 2019, and Sept 17, 2020, 805 patients were enrolled and randomly assigned (402 to the talazoparib group and 403 to the placebo group). Median follow-up for rPFS was 24·9 months (IQR 21·9-30·2) for the talazoparib group and 24·6 months (14·4-30·2) for the placebo group. At the planned primary analysis, median rPFS was not reached (95% CI 27·5 months-not reached) for talazoparib plus enzalutamide and 21·9 months (16·6-25·1) for placebo plus enzalutamide (hazard ratio 0·63; 95% CI 0·51-0·78; p<0·0001). In the talazoparib group, the most common treatment-emergent adverse events were anaemia, neutropenia, and fatigue; the most common grade 3-4 event was anaemia (185 [46%] of 398 patients), which improved after dose reduction, and only 33 (8%) of 398 patients discontinued talazoparib due to anaemia. Treatment-related deaths occurred in no patients in the talazoparib group and two patients (<1%) in the placebo group. INTERPRETATION: Talazoparib plus enzalutamide resulted in clinically meaningful and statistically significant improvement in rPFS versus standard of care enzalutamide as first-line treatment for patients with mCRPC. Final overall survival data and additional long-term safety follow-up will further clarify the clinical benefit of the treatment combination in patients with and without tumour HRR gene alterations. FUNDING: Pfizer.

A Phase I Clinical Trial Evaluating the Safety and Dosing of Relugolix with Novel Hormonal Therapy for the Treatment of Advanced Prostate Cancer.

BACKGROUND: Androgen deprivation therapy (ADT), a cornerstone of prostate cancer treatment, is commonly co-prescribed as combination therapy. OBJECTIVE: To better understand the safety and tolerability profile of relugolix, an oral non-peptide gonadotropin-releasing hormone (GnRH) receptor antagonist, in combination with abiraterone acetate (abiraterone) and apalutamide, a phase I study was undertaken. PATIENTS AND METHODS: This is an ongoing, 52-week, open-label, parallel cohort study of relugolix in combination with abiraterone in men with metastatic castration-sensitive prostate cancer (mCSPC) or metastatic castration-resistant prostate cancer (mCRPC) [Part 1] and apalutamide in men with mCSPC or non-metastatic castration-resistant prostate cancer (nmCRPC) [Part 2]. Eligible patients treated with leuprolide acetate or degarelix with abiraterone or apalutamide prior to baseline, at which time they were transitioned to relugolix. Assessments included reporting of adverse events, clinical laboratory tests, vital sign measurements, electrocardiogram (ECG) parameters, and testosterone serum concentrations. In this interim report, patients completing ≥12 weeks were included. RESULTS: Overall, 15 men were enrolled in Part 1 and 10 in Part 2. Adverse events were mostly mild-to-moderate in intensity and were consistent with the known safety profiles of the individual medications. No transition (from prior ADT treatment)- or time-related trends in clinical laboratory tests, vital sign measurements, or ECG parameters were observed. Mean testosterone concentrations remained below castration levels. CONCLUSIONS: Combination therapy of relugolix and abiraterone or apalutamide was associated with a favorable safety and tolerability profile consistent with the known profiles of the individual medications. Castration levels of testosterone were maintained after transitioning to relugolix from other ADTs. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT04666129.

Plain language summary of the design of the TALAPRO-2 study comparing talazoparib and enzalutamide versus enzalutamide and placebo in men with metastatic castration-resistant prostate cancer.

WHAT IS THIS SUMMARY ABOUT?: This summary describes the design of an ongoing research study (also known as a clinical trial) called TALAPRO-2. The TALAPRO-2 trial is testing the combination of two medicines called talazoparib and enzalutamide as a first treatment in adult men with metastatic castration-resistant prostate cancer. The study began in December 2017 and has enrolled 1037 adult men with metastatic castration-resistant prostate cancer from 26 countries. WHAT IS METASTATIC CASTRATION-RESISTANT PROSTATE CANCER?: Metastatic castration-resistant prostate cancer is a type of cancer that has advanced beyond the prostate and continues to grow even when testosterone levels in the blood are suppressed. WHICH MEDICINES ARE BEING TESTED?: The combination of talazoparib plus enzalutamide will be compared with enzalutamide plus placebo. Enzalutamide is approved to treat men with prostate cancer. Talazoparib is not approved to treat men with prostate cancer. A placebo does not contain any active ingredients and is also known as a sugar pill. WHAT ARE THE AIMS OF THE TALAPRO-2 TRIAL?: The TALAPRO-2 trial will find out if combining talazoparib with enzalutamide increases the length of time the men in the study live without their cancer getting worse compared with enzalutamide plus placebo. The study will also measure how long men in the study live and any side effects the men have while they are taking the study medicines. Researchers are also testing the DNA from the tumor cells of all men in the study to find out if they have faulty DNA repair genes. Clinical Trial Registration: NCT0339519 (ClinicalTrials.gov).

Talazoparib plus enzalutamide in metastatic castration-resistant prostate cancer: TALAPRO-2 phase III study design.

PARP inhibitors in combination with androgen receptor-targeted therapy have demonstrated potential in the treatment of metastatic castration-resistant prostate cancer (mCRPC). Here, we describe the design and rationale of the multinational, phase III, two-part TALAPRO-2 study comparing talazoparib plus enzalutamide versus placebo plus enzalutamide as a first-line treatment for patients with mCRPC with or without DNA damage response (DDR) alterations. This study has two co-primary end points: radiographic progression-free survival (rPFS) by blinded independent clinical review in all-comers (cohort 1) and in patients with DDR alterations (cohort 2). TALAPRO-2 will demonstrate whether talazoparib plus enzalutamide can significantly improve the efficacy of enzalutamide in terms of rPFS in both molecularly unselected and DDR-deficient patients with mCRPC (NCT03395197). Clinical Trial Registration: NCT03395197 (ClinicalTrials.gov).

Enzalutamide versus bicalutamide in patients with nonmetastatic castration-resistant prostate cancer: a prespecified subgroup analysis of the STRIVE trial.

BACKGROUND: In the phase 2, randomized, double-blind STRIVE trial, enzalutamide significantly reduced the risk of prostate cancer progression or death versus bicalutamide in patients with metastatic castration-resistant prostate cancer (mCRPC) and nonmetastatic CRPC (nmCRPC). The objective of this protocol-specified subgroup analysis of STRIVE was to investigate the benefit of enzalutamide versus bicalutamide specifically in patients with nmCRPC. METHODS: Patients (N = 139) were stratified by disease stage and randomized to enzalutamide 160 mg/day plus androgen deprivation therapy (ADT; n = 70) or bicalutamide 50 mg/day plus ADT (n = 69). RESULTS: Baseline characteristics of patients with nmCRPC were comparable between groups. At a median of 17 months follow-up, enzalutamide reduced the risk of progression or death by 76% versus bicalutamide in patients with nmCRPC (hazard ratio [HR], 0.24; 95% CI 0.14-0.42). Enzalutamide reduced risk of prostate-specific antigen progression by 82% versus bicalutamide in patients with nmCRPC (HR, 0.18; 95% CI 0.10-0.34). The most frequently reported adverse events by patients receiving enzalutamide were fatigue (36.2%), hot flush (20.3%), decreased appetite (17.4%), dizziness (17.4%), and nausea (17.4%). CONCLUSIONS: This STRIVE subgroup analysis of patients with nmCRPC illustrates the benefit of enzalutamide in reducing the risk of progression or death versus bicalutamide in patients with nmCRPC. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT01664923.

Optimizing the management of castration-resistant prostate cancer patients: A practical guide for clinicians.

BACKGROUND: Advanced prostate cancer (PC) patients, especially those with metastatic prostate cancer (mPC), often require complex management pathways. Despite the publication of clinical practice guidelines by leading urological and oncological organizations that provide a substantial and comprehensive framework, there are numerous clinical scenarios that are not always addressed, especially as new treatments become available, new imaging modalities are developed, and advances in genetic testing continue. METHODS: A 14-member expert review panel comprised of urologists and medical oncologists were chosen to provide guidance on addressing specific topics and issues regarding metastatic castration-resistant prostate cancer (mCRPC) patients. Panel members were chosen based upon their experience and expertise in the management of PC patients. Four academic members (two urologists and two medical oncologists) of the panel served as group leaders; the remaining eight panel members were from Large Urology Group Practice Association (LUGPA) practices with proven experience in leading their advanced PC clinics. The panel members were assigned to four separate working groups, each assigned a specific mCRPC topic to review and discuss with the entire panel. RESULTS: This article describes the practical recommendations of an expert panel on the management of mCRPC patients. The target reading audience for this publication is all providers (urologists, medical oncologists, radiation oncologists, or advanced practice providers) who evaluate and manage advanced PC patients, regardless of their practice setting. CONCLUSION: The panel has provided recommendations for managing mCRPC with regard to specific issues: (a) biomarker monitoring and the role of genetic and molecular testing; (b) rationale, current strategies, and optimal sequencing of the various approved therapies, including hormonal therapy, cytotoxic chemotherapy, radiopharmaceuticals and immunotherapy; (c) adverse event management and monitoring; and (d) imaging advanced PC patients. These recommendations seek to complement national guidelines, not replace them, and a discussion of where the panel agreed or disagreed with national guidelines is included.

Effect of Enzalutamide plus Androgen Deprivation Therapy on Health-related Quality of Life in Patients with Metastatic Hormone-sensitive Prostate Cancer: An Analysis of the ARCHES Randomised, Placebo-controlled, Phase 3 Study.

BACKGROUND: In the ARCHES study in metastatic hormone-sensitive prostate cancer (mHSPC), enzalutamide plus androgen deprivation therapy (ADT) improved radiographic progression-free survival (rPFS) versus ADT alone. OBJECTIVE: To evaluate patient-reported outcomes (PROs) to week 73. DESIGN, SETTING, AND PARTICIPANTS: ARCHES (NCT02677896) was a randomised, double-blind, placebo-controlled, phase 3 study in mHSPC patients. INTERVENTION: Enzalutamide (160 mg/day) plus ADT or placebo plus ADT. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: PROs were assessed at baseline, week 13, and every 12 wk until disease progression using the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Prostate 25 (QLQ-PR25), Functional Assessment of Cancer Therapy-Prostate (FACT-P), Brief Pain Inventory Short Form, and EuroQoL 5-Dimensions, 5-Levels (EQ-5D-5 L) instruments. Endpoints included time to first (TTFD) and first confirmed (TTFCD) clinically meaningful deterioration (using predefined questionnaire thresholds) in health-related quality of life (HRQoL) and pain. RESULTS AND LIMITATIONS: A total of 1150 patients received ADT plus enzalutamide (n = 574) or placebo (n = 576). Baseline PRO scores indicated high HRQoL and low pain, which was generally maintained in both groups. There were no statistically significant (nominal p > 0.05) between-group differences that occurred in both TTFD and TTFCD together for QLQ-PR25 and FACT-P scores. Enzalutamide significantly delayed TTFD in worst pain (by ∼3 mo; nominal p = 0.032), pain severity (nominal p = 0.021), and EQ-5D-5 L visual analogue scale score (nominal p = 0.0070) versus placebo (not significant for confirmed deterioration for pain outcomes). Enzalutamide delays deterioration in several HRQoL subscales and pain severity in high-volume disease. CONCLUSIONS: Enzalutamide plus ADT enables men with mHSPC to maintain high-functioning HRQoL and low symptom burden. PATIENT SUMMARY: This study examined the effect on health-related quality of life and pain of adding enzalutamide or placebo to androgen deprivation therapy for patients with metastatic hormone-sensitive prostate cancer. Addition of enzalutamide allowed patients to maintain their health-related quality of life.

Enzalutamide Versus Bicalutamide in Castration-Resistant Prostate Cancer: The STRIVE Trial.

PURPOSE: Enzalutamide, a potent oral androgen receptor inhibitor, improves survival in men with metastatic castration-resistant prostate cancer (CRPC) before and after chemotherapy. Bicalutamide, a nonsteroidal antiandrogen, is widely used to treat men with nonmetastatic or metastatic CRPC. The efficacy and safety of these drugs were compared in this randomized, double-blind, phase II study of men with CRPC. PATIENTS AND METHODS: A total of 396 men with nonmetastatic (n = 139) or metastatic (n = 257) CRPC were randomly assigned to enzalutamide 160 mg per day (n = 198) or bicalutamide 50 mg per day (n = 198). Androgen deprivation therapy was continued in both arms. The primary end point was progression-free survival (PFS). RESULTS: Enzalutamide reduced the risk of progression or death by 76% compared with bicalutamide (hazard ratio [HR], 0.24; 95% CI, 0.18 to 0.32; P < .001). Median PFS was 19.4 months with enzalutamide versus 5.7 months with bicalutamide. Enzalutamide resulted in significant improvements in all key secondary end points: time to prostate-specific antigen progression (HR, 0.19; 95% CI, 0.14 to 0.26; P < .001); proportion of patients with a ≥ 50% prostate-specific antigen response (81% v 31%; P < .001); and radiographic PFS in metastatic patients (HR, 0.32; 95% CI, 0.21 to 0.50; P < .001). Beneficial effects with enzalutamide were observed in both nonmetastatic and metastatic subgroups. The observed adverse event profile was consistent with that from phase III enzalutamide trials. CONCLUSION: Enzalutamide significantly reduced risk of prostate cancer progression or death compared with bicalutamide in patients with nonmetastatic or metastatic CRPC.