Niraparib and Abiraterone Acetate for Metastatic Castration-Resistant Prostate Cancer

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].

Phase 3 MAGNITUDE study: First results of niraparib (NIRA) with abiraterone acetate and prednisone (AAP) as first-line therapy in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) with and without homologous recombination repair (HRR) gene alterations

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Background: Approximately 20% of mCRPC has alterations in genes associated with HRR and is responsive to PARP inhibitors (PARPi) such as NIRA. Combined PARPi with androgen receptor pathway targeting may also benefit unselected mCRPC. MAGNITUDE assessed whether adding NIRA to AAP improves outcomes in pts with mCRPC with or without alterations in HRR associated genes. Methods: MAGNITUDE (NCT03748641) is a randomized, double-blind phase 3 study. In eligible mCRPC pts, ≤4 mos of prior AAP for mCRPC was allowed. Pts with (HRR biomarker [BM]+; ATM, BRCA1, BRCA2, BRIP1, CDK12, CHEK2, FANCA, HDAC2, PALB2) and without specified gene alterations (HRR BM-) were randomized 1:1 to receive NIRA 200 mg once daily + AAP or placebo (PBO) + AAP. Primary endpoint was radiographic progression-free survival (rPFS) assessed by blinded independent central review (BICR) in the BRCA1/2 group followed by all HRR BM+ pts. Secondary endpoints were time to initiation of cytotoxic chemotherapy (TTCC), time to symptomatic progression (TTSP) and overall survival (OS). Other endpoints included time to PSA progression (TTPP) and objective response rate (ORR). Results: 423 HRR BM+ pts were randomized to NIRA + AAP (n = 212) or PBO + AAP (n = 211). Median age was 69, 23% had prior AAP, 21% had visceral metastases, and 53% had BRCA1/2 mutations. Median follow-up was 18.6 mos. NIRA + AAP significantly improved rPFS by BICR in the BRCA1/2 subgroup and in all HRR BM+ pts, reducing the risk of progression or death by 47% (16.6 vs 10.9 mo) and 27% (16.5 vs 13.7 mo) respectively (Table), vs PBO + AAP. Investigator assessed rPFS was consistent with BICR. NIRA + AAP delayed TTCC, TTSP, and TTPP and improved ORR in HRR BM+ pts (Table). First interim analysis of OS is immature. The preplanned futility analysis in 233 HRR BM- pts showed no benefit of adding NIRA to AAP in the prespecified composite endpoint (first of PSA progression or rPFS; HR, 1.09; 95% CI, 0.75-1.57). No new safety signals were seen. In HRR BM+ pts, 67% and 46.4% had grade 3/4 AEs and 9% and 3.8% discontinued treatment in the NIRA + AAP and PBO + AAP arms, respectively. There were no clinically significant differences in overall quality of life (FACT-P). Conclusions: NIRA + AAP improves rPFS and other clinically relevant outcomes in pts with mCRPC and alterations in HRR associated genes. There was no evidence of benefit with the addition of NIRA to AAP in HRR BM- pts with mCRPC. Clinical trial information: NCT03748641. [Table: see text]