PURPOSE: The first interim analysis of the phase III, randomized, placebo-controlled TITAN study showed that apalutamide significantly improved overall survival (OS) and radiographic progression-free survival in patients with metastatic castration-sensitive prostate cancer (mCSPC) receiving ongoing androgen deprivation therapy (ADT). Herein, we report final efficacy and safety results after unblinding and placebo-to-apalutamide crossover. METHODS: Patients with mCSPC (N = 1,052) were randomly assigned 1:1 to receive apalutamide (240 mg QD) or placebo plus ADT. After unblinding in January 2019, placebo-treated patients were allowed to receive apalutamide. Efficacy end points were updated using the Kaplan-Meier method and Cox proportional-hazards model without formal statistical retesting and adjustment for multiplicity. Change from baseline in Functional Assessment of Cancer Therapy-Prostate total score was assessed. RESULTS: With a median follow-up of 44.0 months, 405 OS events had occurred and 208 placebo-treated patients (39.5%) had crossed over to apalutamide. The median treatment duration was 39.3 (apalutamide), 20.2 (placebo), and 15.4 months (crossover). Compared with placebo, apalutamide plus ADT significantly reduced the risk of death by 35% (median OS not reached v 52.2 months; hazard ratio, 0.65; 95% CI, 0.53 to 0.79; P < .0001) and by 48% after adjustment for crossover (hazard ratio, 0.52; 95% CI, 0.42 to 0.64; P < .0001). Apalutamide plus ADT delayed second progression-free survival and castration resistance ( P < .0001 for both). Health-related quality of life, per total Functional Assessment of Cancer Therapy-Prostate, in both groups was maintained through the study. Safety was consistent with previous reports. CONCLUSION: The final analysis of TITAN confirmed that, despite crossover, apalutamide plus ADT improved OS, delayed castration resistance, maintained health-related quality of life, and had a consistent safety profile in a broad population of patients with mCSPC.

Primary resistance to androgen receptor (AR)–directed therapies in metastatic castration-resistant prostate cancer (mCRPC) is poorly understood. We randomized 202 patients with treatment-naïve mCRPC to abiraterone or enzalutamide and performed whole-exome and deep targeted 72-gene sequencing of plasma cell-free DNA prior to therapy. For these agents, which have never been directly compared, time to progression was similar. Defects in BRCA2 and ATM were strongly associated with poor clinical outcomes independently of clinical prognostic factors and circulating tumor DNA abundance. Somatic alterations in TP53, previously linked to reduced tumor dependency on AR signaling, were also independently associated with rapid resistance. Although detection of AR amplifications did not outperform standard prognostic biomarkers, AR gene structural rearrangements truncating the ligand binding domain were identified in several patients with primary resistance. These findings establish genomic drivers of resistance to first-line AR-directed therapy in mCRPC and identify potential minimally invasive biomarkers. Significance: Leveraging plasma specimens collected in a large randomized phase II trial, we report the relative impact of common circulating tumor DNA alterations on patient response to the most widely used therapies for advanced prostate cancer. Our findings suggest that liquid biopsy analysis can guide the use of AR-targeted therapy in general practice. Cancer Discov; 8(4); 444–57. ©2018 AACR. See related commentary by Jayaram et al., p. 392. This article is highlighted in the In This Issue feature, p. 371

Purpose: Although novel agents targeting the androgen–androgen receptor (AR) axis have altered the treatment paradigm of metastatic castration-resistant prostate cancer (mCRPC), development of therapeutic resistance is inevitable. In this study, we examined whether AR gene aberrations detectable in circulating cell-free DNA (cfDNA) are associated with resistance to abiraterone acetate and enzalutamide in mCRPC patients. Experimental Design: Plasma was collected from 62 mCRPC patients ceasing abiraterone acetate (n = 29), enzalutamide (n = 19), or other agents (n = 14) due to disease progression. DNA was extracted and subjected to array comparative genomic hybridization (aCGH) for chromosome copy number analysis, and Roche 454 targeted next-generation sequencing of exon 8 in the AR. Results: On aCGH, AR amplification was significantly more common in patients progressing on enzalutamide than on abiraterone or other agents (53% vs. 17% vs. 21%, P = 0.02, χ²). Missense AR exon 8 mutations were detected in 11 of 62 patients (18%), including the first reported case of an F876L mutation in an enzalutamide-resistant patient and H874Y and T877A mutations in 7 abiraterone-resistant patients. In patients switched onto enzalutamide after cfDNA collection (n = 39), an AR gene aberration (copy number increase and/or an exon 8 mutation) in pretreatment cfDNA was associated with adverse outcomes, including lower rates of PSA decline ≥ 30% (P = 0.013, χ²) and shorter time to radiographic/clinical progression (P = 0.010, Cox proportional hazards regression). Conclusions: AR gene aberrations in cfDNA are associated with resistance to enzalutamide and abiraterone in mCRPC. Our data illustrate that genomic analysis of cfDNA is a minimally invasive method for interrogating mechanisms of therapeutic resistance in mCRPC. Clin Cancer Res; 21(10); 2315–24. ©2015 AACR.

PURPOSE: Metastatic castration-resistant prostate cancer (mCRPC) remains a lethal disease with current standard-of-care therapies. Homologous recombination repair (HRR) gene alterations, including BRCA1/2 alterations, can sensitize cancer cells to poly (ADP-ribose) polymerase inhibition, which may improve outcomes in treatment-naïve mCRPC when combined with androgen receptor signaling inhibition.METHODS: MAGNITUDE (ClinicalTrials.gov identifier: NCT03748641 ) is a phase III, randomized, double-blinded study that evaluates niraparib and abiraterone acetate plus prednisone (niraparib + AAP) in patients with (HRR+, n = 423) or without (HRR−, n = 247) HRR-associated gene alterations, as prospectively determined by tissue/plasma-based assays. Patients were assigned 1:1 to receive niraparib + AAP or placebo + AAP. The primary end point, radiographic progression-free survival (rPFS) assessed by central review, was evaluated first in the BRCA1/2 subgroup and then in the full HRR+ cohort, with secondary end points analyzed for the full HRR+ cohort if rPFS was statistically significant. A futility analysis was preplanned in the HRR− cohort.RESULTS: Median rPFS in the BRCA1/2 subgroup was significantly longer in the niraparib + AAP group compared with the placebo + AAP group (16.6 v 10.9 months; hazard ratio [HR], 0.53; 95% CI, 0.36 to 0.79; P = .001). In the overall HRR+ cohort, rPFS was significantly longer in the niraparib + AAP group compared with the placebo + AAP group (16.5 v 13.7 months; HR, 0.73; 95% CI, 0.56 to 0.96; P = .022). These findings were supported by improvement in the secondary end points of time to symptomatic progression and time to initiation of cytotoxic chemotherapy. In the HRR− cohort, futility was declared per the prespecified criteria. Treatment with niraparib + AAP was tolerable, with anemia and hypertension as the most reported grade ≥ 3 adverse events.CONCLUSION: Combination treatment with niraparib + AAP significantly lengthened rPFS in patients with HRR+ mCRPC compared with standard-of-care AAP.[Media: see text]

Prostate cancer cells are initially reliant on circulating androgens binding and activating the endogenous androgen receptor (AR). Although androgen deprivation therapy elicits a response in most patients, progression to castration-resistant prostate cancer (CRPC), driven frequently by AR reactivation, is inevitable.¹ However, in recent years, continued targeting of the AR signaling axis with abiraterone acetate and enzalutamide has changed clinical practice and improved the overall survival of patients with CRPC.^2-5 Multiple other AR axis inhibitors are in clinical trials, promising to expand the arsenal available to patients.⁶