Adding the DNA-repair–targeting drug niraparib to standard hormone therapy early in treatment may significantly delay disease progression for men with metastatic castration-sensitive prostate cancer (mCSPC) carrying homologous recombination repair (HRR) gene alterations, according to new results published in Nature Medicine from the Phase III AMPLITUDE trial.
New strategy for an old challenge
For decades, the mainstay treatment for mCSPC has been androgen deprivation therapy (ADT)—cutting off the hormones that fuel tumor growth. But while many patients initially respond, relapse is nearly inevitable.
Those whose tumors harbor HRR gene alterations, including mutations in BRCA1, BRCA2, or ATM, face a particularly aggressive course. These genes normally help cells repair damaged DNA through a process called homologous recombination repair. When they malfunction, cancer cells accumulate DNA errors, which can both accelerate tumor growth and create a specific weakness that drugs called PARP inhibitors can exploit.
PARP inhibitors, such as niraparib or olaparib, block a secondary DNA-repair pathway. When both repair routes are disabled, cancer cells are unable to fix their DNA and die. Historically, these drugs have been used only after hormone resistance develops—but by then, resistance to PARP inhibition itself often follows.
Testing PARP inhibition early
The AMPLITUDE trial explored whether targeting this vulnerability earlier—within six months of starting ADT—could improve outcomes. The study enrolled 696 men with mCSPC and HRR mutations, randomly assigning them to niraparib plus abiraterone acetate and prednisone (AAP) or AAP plus placebo.
Participants had high-risk disease: over half carried BRCA1 or BRCA2 mutations, 78% had extensive metastases, and 16% had previously received chemotherapy. The main goal was to measure radiographic progression-free survival (rPFS)—the time before imaging showed new or worsening disease.
Progression delayed, symptoms reduced
Results were compelling. Among men with BRCA1 or BRCA2 mutations, median rPFS was not reached in the niraparib group but only 26 months with placebo, representing a 48% reduction in risk of progression or death. Overall, niraparib reduced the risk of cancer growth by 37% compared to AAP alone in all patients.
Across all HRR-altered patients, the benefit remained strong. Patients on niraparib also reported delayed onset of symptoms and better overall quality of life during early treatment cycles.
The authors concluded that combining PARP inhibition with hormonal therapy early—before resistance sets in—can meaningfully extend the time patients live without progression, adding that the approach is a compelling case for rethinking the sequence of treatment for HRR-mutant prostate cancer.
Toxicity was consistent with known effects of PARP inhibition. Grade 3 or 4 adverse events occurred in 75% of patients on niraparib compared with 59% on placebo.
Encouragingly, patients’ quality-of-life scores improved after the initial treatment cycles, and early overall survival data showed a 21% reduction in the risk of death; however, longer follow-up is needed for confirmation.
PARP inhibitors have already transformed care for castration-resistant prostate cancer, a disease that no longer responds to hormonal therapy. The AMPLITUDE trial extends that success to the hormone-sensitive setting, suggesting that earlier intervention could postpone the inevitable transition to resistance.
