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.

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e14521 Background: Thestandard treatment for biliary tract cancer is gemcitabine plus platinum, but median progression-free survival (PFS) is only 5-8 months (m) (Valle et al, NEJM 2010). Gene expression or somatic mutations may influence the clinical phenotype, which will affect decisions on individualized treatment. Methods: We retrospectively analyzed tissue blocks from 54 advanced or metastatic cholangiocarcinoma, gallbladder or ampulllary cancer patients (p) treated with single-agent gemcitabine or gemcitabine plus carboplatin or cisplatin. Using RT-PCR, we analyzed the mRNA expression levels of oncogenes, tumor suppressors and DNA repair genes (BRCA1, RRM1, AEG-1, RAP80, SPINK1 and FBXW7) and correlated results with PFS, overall survival (OS) and response. In addition, FBXW7 hotspot mutations were assessed. Results: p characteristics: 72% females; median age, 60 (40-87). Only FBXW7 expression correlated with PFS and OS. When FBXW7 levels were dichotomized at the median value, PFS was 4.2 m for p with low levels vs 12.6 m for p with high levels (p=0.02). When FBXW7 expression was divided by terciles, PFS was 4.9 m for p in the lowest tercile, 7.6 for p in the intermediate tercile, and 26.9 m for p in the highest tercile (p=0.08). OS was 6.2 m for p in the lowest tercile, 8 m for p in the intermediate tercile, and not reached for p in the highest tercile. No other significant correlation was observed between expression levels of the other genes examined and PFS or OS. Only AEG-1 expression correlated with response (p=0.05). No FBXW7 hotspot mutations were detected. Conclusions: Although we did not find the FBXW7 hotspot mutations previously described in biliary tract cancer, FBXW7 mRNA expression significantly influenced PFS and OS. A separate cohort of p is being analyzed to validate the prognostic role of FBXW7.