A phase II trial of trabectedin in triple-negative and HER2-overexpressing metastatic breast cancer

Trabectedin is an alkylating agent that binds to the minor groove of DNA. Early studies with trabectedin suggested efficacy in triple-negative and HER2-overexpressing metastatic breast cancer (MBC). The efficacy and safety of trabectedin in pretreated patients with these tumors were evaluated in this parallel-cohort phase II trial. Patients received a 3-h infusion of trabectedin 1.3 mg/m² intravenously every 3 weeks until progression or unmanageable/unacceptable toxicity. The primary objective was to evaluate the efficacy using the objective response rate (ORR) as per Response Evaluation Criteria In Solid Tumors (RECIST). Secondary objectives comprised time-to-event endpoints and safety assessed with the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) v.3.0. Patients with heavily pretreated triple-negative (n = 50) or HER2-overexpressing (n = 37) MBC were enrolled. No confirmed responses were found in triple-negative MBC patients, with median progression-free survival (PFS) of 2.2 months (95 % CI 1.3–2.7 months). Confirmed partial responses occurred in 4 of 34 evaluable HER2-overexpressing MBC patients (ORR = 12 %; 95 % CI 3–27 %) and lasted a median of 12.5 months (95 % CI, 6.2–14.7 months); median PFS was 3.8 months (95 % CI, 1.8–5.5 months). Most trabectedin-related adverse events were mild or moderate, and the most frequent were fatigue, nausea, vomiting, constipation, and anorexia. Severe neutropenia and transaminase increases were non-cumulative and transient and were mostly managed by infusion delays or dose reductions. Single-agent trabectedin is well tolerated in aggressive MBC and has moderate activity in HER2-overexpressing tumors. Further studies are warranted to evaluate trabectedin combined with HER2-targeted treatments in this subtype.