Combination of niraparib + abiraterone acetate + prednisone significantly improved radiographic progression-free survival as a first-line therapy in HRR gene-mutated metastatic castration-resistant prostate cancer.

At the final analysis for radiographic progression-free survival (rPFS), the treatment combination of niraparib and abiraterone acetate plus prednisone demonstrated a statistically significant improvement in patients with HRR gene alterations. Results were featured in a late-breaking oral presentation (Abstract #12; Oral Abstract Session A) at the American Society of Clinical Oncology’s Genitourinary (ASCO GU) Cancers Symposium,in San Francisco and virtually from February 17-19, 2022.

MAGNITUDE (NCT03748641) is a Phase III, randomized, double-blind, placebo-controlled, multicenter study evaluating the safety and efficacy of the combination of niraparib and abiraterone acetate plus prednisone as a first-line therapy in patients with mCRPC. The MAGNITUDE study was intentionally designed with two independent cohorts to assess treatment effect in patients with and without HRR gene alterations (including ATM, BRCA1, BRCA2, BRIP1, CDK12, CHEK2, FANCA, HDAC2, PALB2 alterations) versus standard of care.

The cohort of patients with prospectively-identified HRR gene alterations enrolled 423 patients, with patients randomized to receive the combination of niraparib and abiraterone acetate plus prednisone (combination arm [n=212]) or placebo and abiraterone acetate plus prednisone (control arm [n=211]). At 18.6-month median follow-up, patients in the combination arm of the cohort with HRR gene alterations showed a significant improvement in rPFS, with a reduction in the risk of progression or death of 27 percent (hazard ratio [HR] 0.73; p=0.022). This improvement was most pronounced in patients with BRCA1/2 gene alterations, where a 47 percent risk reduction was observed for rPFS (HR 0.53; p=0.001), as analyzed by blinded independent central review (BICR). A consistent but greater improvement was observed in investigator-assessed rPFS, which showed an overall 36 percent risk reduction in patients with HRR gene alterations (HR: 0.64; p=0.002), and a 50 percent risk reduction in patients with BRCA1/2 gene alterations (HR: 0.50; p=0.0006).

The cohort without HRR gene alterations (n=233) met the predefined futility criteria in August 2020, showing no benefit from the treatment combination (HR>1) in the HRR biomarker negative population. Enrollment into this cohort was stopped at the time of futility at the recommendation of the Independent Data Monitoring Committee. Investigators and patients were unblinded and given the opportunity to continue treatment with niraparib and abiraterone acetate plus prednisone or receive only abiraterone acetate plus prednisone at the discretion of the study investigator.

“When choosing a treatment plan for patients with prostate cancer, physicians must consider individual needs, particularly for patients with mCRPC with HRR gene alterations who face a poor prognosis,” said Dr. Kim Chi, Medical Oncologist at BC Cancer - Vancouver and principal investigator of the MAGNITUDE study. “The MAGNITUDE data provide important context about the subgroup of patients with prostate cancer who may benefit from treatment with niraparib in combination with abiraterone acetate plus prednisone in the first-line setting, as well as those who may be better served by other treatment options.”

In patients with HRR gene alterations, clinically relevant improvements in outcomes were also seen at this first interim analysis for secondary endpoints including time to initiation of cytotoxic chemotherapy, time to symptomatic progression and time to PSA progression. Additionally, objective response rate was improved by the combination of niraparib and abiraterone acetate plus prednisone. Overall survival data were immature at this interim analysis and follow-up will continue for all secondary endpoints.

The observed safety profile of the combination of niraparib and abiraterone acetate plus prednisone was consistent with the known safety profile of each agent. Of the patients with HRR gene alterations, 67 percent experienced Grade 3 adverse events (AEs) and 46.4 percent experienced Grade 4 AEs, largely driven by anemia and fatigue. Discontinuation rates for the combination arm and control arm were 10.8 percent and 4.7 percent respectively. The combination of niraparib and abiraterone acetate plus prednisone also maintained overall quality of life in comparison with placebo and abiraterone acetate plus prednisone as measured on the Functional Assessment of Cancer Therapy–Prostate (FACT-P) scale.

Patients with HRR gene alterations, such as BRCA1/2, are at an increased risk of developing prostate cancer, and BRCA-related prostate cancer is usually aggressive. Long-term survival is low for patients with mCRPC and those who have HRR gene alterations face a worse prognosis, driving a significant unmet medical need for novel therapies in this disease.