PRIMA/ENGOT-OV26/GOG-3012

Prof Antonio González Martín, medical oncologist and director of the Cancer Center at the University of Navarra, presented long-term results from the PRIMA-ENGOT-OB26-GLG3012 study.

This phase III trial involved patients with high-grade serous and endometrioid ovarian cancers who responded to platinum-based chemotherapy. Patients were randomised 2:1 to receive daily niraparib or placebo for up to 36 months or until disease progression. The primary endpoint was PFS, with OS as a key secondary endpoint, evaluated when 60% of events were reached.

The PRIMA study focused on a high-risk population prone to relapse. In the long-term analysis, niraparib demonstrated a sustained PFS benefit, particularly in HRd-positive patients. At five years, HRd-positive patients on niraparib were twice as likely to be progression-free compared to those on placebo, with a 20% higher chance of being relapse-free. The PFS curves between niraparib and placebo remained separated, confirming its long-term benefit.

However, the updated OS data showed no significant difference between the two arms, with a hazard ratio of 1.01, indicating no OS benefit. This finding held true across biomarker groups, including HRd and HRp populations, where OS differences were minimal. Despite this, a surprisingly high number of patients, in both the niraparib and placebo arms, remained alive at five years, which exceeded expectations.

Several factors could explain this long-term survival. In the HRd group, patients in the placebo arm had a median post-progression survival of five years, likely influenced by subsequent therapies, including PARP inhibitors. Up to 60% of BRCA-mutated patients in the placebo arm received post-trial PARP inhibitors, which may have contributed to the extended survival seen in the study.

The safety profile of niraparib remained consistent with prior findings. An individualised starting dose led to lower haematological toxicity compared to a fixed dose. The incidence of myelodysplastic syndrome and acute myeloid leukemia was low, at 2.3% with niraparib and 1.6% with placebo.

In conclusion, the PRIMA trial confirms niraparib as an effective maintenance therapy, particularly in HRd-positive patients, by providing sustained PFS benefit. Although no OS benefit was observed, the drug remains a valuable first-line option for patients across biomarker populations. The long-term safety profile is consistent with previous data, making niraparib a viable standard of care for ovarian cancer maintenance therapy.