For patients carrying rare DNA-repair gene mutations in cancers that fall outside olaparib's approved indications, treatment options after standard therapies are typically exhausted. This basket trial signals that the PARP inhibitor's reach may extend meaningfully beyond its current BRCA1/2 label — a finding with real implications for tumor-agnostic precision oncology.
This investigator-initiated, open-label Phase II basket trial enrolled patients with advanced, treatment-refractory solid tumors stratified by germline or somatic mutations in homologous recombination (HR) genes. Across a broad panel of 19 HR-related genes — including ATR, CDK12, CHEK1, RAD51C, RAD51D, POLE, and others — no objective responses were observed. However, four gene cohorts stood apart: BAP1, BARD1, BRIP1, and PALB2 mutations, whether somatic or germline in origin, were each associated with measurable clinical responses to olaparib across histologically diverse cancer types. The trial's design deliberately separated somatic from germline mutation carriers, providing a more granular view of which mutational contexts actually drive PARP inhibitor sensitivity.
This result is clinically significant because PALB2 has been a known moderate-risk BRCA-interacting gene, but BAP1 and BARD1 have had a murkier relationship with HRD-based therapies in clinical practice. The complete absence of responses across 19 other HR pathway genes is equally informative — it challenges the assumption that any mutation touching the homologous recombination pathway confers olaparib sensitivity, and argues against broad, undifferentiated HRD biomarker panels as predictive tools. The basket design, while efficient for rare alterations, carries inherent limitations: cohort sizes are likely small and heterogeneous by tumor type, making effect-size estimates imprecise and statistical power limited. This should be considered hypothesis-generating rather than practice-changing, requiring prospective validation in larger, gene-specific cohorts. Still, for a precision oncology field struggling with the long tail of rare genomic variants, identifying even four actionable HRD genes outside BRCA1/2 represents a meaningful, if incremental, advance.