Higher antitumor activity of trabectedin in germline BRCA2 carriers with advanced breast cancer as compared to BRCA1 carriers: A subset analysis of a dedicated phase II trial

Specific alkylators may allow synthetic lethality among patients with germline BRCA1/2-mutations related cancers. The tetrahydroisoquinolone trabectedin administered at 1.3 mg/m2 as a 3-h intravenous infusion every 3 weeks showed activity in patients with pretreated metastatic breast cancer (MBC) and BRCA germline mutations, but mainly in BRCA2 carriers. Data from a phase II study were retrospectively analyzed to compare the efficacy and safety of this trabectedin dose and schedule in pretreated MBC patients bearing germline BRCA1/2 mutations. The primary efficacy endpoint was the objective response rate (ORR) as per Response Evaluation Criteria In Solid Tumors (RECIST) by independent expert review. Duration of response (DR) and progression-free survival (PFS) were secondary efficacy endpoints. Safety was evaluated using the National Cancer Institute Common Toxicity Criteria (NCI-CTC). Data from 26 BRCA1-mutated and 13 BRCA2-mutated patients were analyzed. 69% of BRCA1-mutated cancers were triple-negative vs. 31% of BRCA2-mutated ones. 77% of BRCA1 and 31% of BRCA2 carriers were platinum-pretreated. The ORR in BRCA2-mutated patients was higher than in BRCA1-mutated patients (33.3% vs. 9.1%). DR ranged for 1.4-6.8 months in BRCA2-mutated patients and for 1.5-1.7 months in BRCA1-mutated patients. More BRCA2-mutated patients had disease stabilization for ≥4 months (25.0% vs. 9.1%) and their median PFS was longer (4.7 vs. 2.5 months). Trabectedin was well tolerated in both patient subtypes. In conclusion, trabectedin showed higher antitumor activity in relapsed MBC patients with germline BRCA2 mutations than in those with BRCA1 mutations.