Long-Term Responders on Olaparib Maintenance in High-Grade Serous Ovarian Cancer: Clinical and Molecular Characterization.

Maintenance therapy with olaparib has improved progression-free survival in women with high-grade serous ovarian cancer (HGSOC), particularly those harboring mutations. The objective of this study was to characterize long-term (LT) versus short-term (ST) responders to olaparib. A comparative molecular analysis of Study 19 (NCT00753545), a randomized phase II trial assessing olaparib maintenance after response to platinum-based chemotherapy in HGSOC, was conducted. LT response was defined as response to olaparib/placebo >2 years, ST as <3 months. Molecular analyses included germline status, three-biomarker homologous recombination deficiency (HRD) score, methylation, and mutational profiling. Another olaparib maintenance study (Study 41; NCT01081951) was used as an additional cohort. Thirty-seven LT (32 olaparib) and 61 ST (21 olaparib) patients were identified. Treatment was significantly associated with outcome ( < 0.0001), with more LT patients on olaparib (60.4%) than placebo (11.1%). LT sensitivity to olaparib correlated with complete response to chemotherapy ( < 0.05). In the olaparib LT group, 244 genetic alterations were detected, with , and mutations being most common (90%, 25%, and 35%, respectively). mutations were enriched among the LT responders. methylation was not associated with response duration. High myriad HRD score (>42) and/or mutation was associated with LT response to olaparib. Study 41 confirmed the correlation of LT response with olaparib and mutation. Findings show that LT response to olaparib may be multifactorial and related to homologous recombination repair deficiency, particularly defects. The type of mutation warrants further investigation. .