Olaparib Use in Patients With Metastatic Breast Cancer Harboring Somatic BRCA1/2 Mutations or Mutations in Non-BRCA1/2, DNA Damage Repair Genes

Poly-ADP ribose polymerase (PARP) inhibitors (PARPi) are active in patients with germline BRCA1/2 (gBRCA1/2)-mutated breast cancer, accounting for 5% to 10% of all breast cancers. Another 5% to 10% harbor somatic BRCA1/2 (sBRCA1/2) mutations or mutations in non-BRCA1/2, homologous recombination repair (HRR) genes but until recently, there were no data for the use of PARPi in these patients. This study examines the use of olaparib in patients with metastatic breast cancer harboring sBRCA1/2 or germline or somatic non-BRCA1/2, HRR mutations and demonstrates potential activity of PARPi in this setting.In this retrospective, single institution study, patients who were treated with off-label, off-protocol olaparib for metastatic breast cancer harboring sBRCA1/2 or germline or somatic non-BRCA1/2, HRR mutations were identified. The primary aim was to describe these patients' demographics, tumor characteristics, mutations, safety and tolerability, response rates, progression free survival, PARPi-associated survival and subsequent treatment.Seven patients were treated off-label, off-trial with olaparib for sBRCA1/2-mutated cancers (n = 4) or non-BRCA1/2, HRR-mutated cancers (n = 3). All patients with sBRCA1/2-mutated cancers responded to PARP inhibition; patients with non-BRCA1/2, HRR-mutated cancers did not respond. The median progression free survival in patients with a sBRCA1/2 mutation was 6.5 months (range 5-9 months) vs. 3 months (range 2-4 months) in patients with non-BRCA1/2, HRR mutations.This single institution experience adds to recent larger reports confirming evidence for PARPi therapy in patients with metastatic breast cancer harboring sBRCA1/2 mutations. No activity was observed in patients with either germline or somatic non-BRCA1/2, HRR-mutated cancers.