Purpose: Human epidermal growth factor receptor 2 (HER2) overexpression is associated with a more aggressive form of breast cancer that responds well to trastuzumab therapy. Trastuzumab-based combination regimens have shown greater antitumor activity than chemotherapy alone. These findings, coupled with the favorable antitumor activity and tolerability profile of vinorelbine in breast cancer, provided the rationale for investigating the novel combination of vinorelbine and trastuzumab.
Patients and methods: A phase II, open-label trial of intravenous vinorelbine (30 mg/m(2) on day 1, then weekly) and trastuzumab (4 mg/kg on day 0, then 2 mg/kg weekly) was conducted in previously untreated HER2(+) metastatic breast cancer patients. Vinorelbine dose was adjusted for grade 3/4 neutropenia; patients remained on combination therapy until disease progression or patient withdrawal due to adverse events.
Results: Of 40 enrolled patients (median age 51 years, range 30-82), 37 were evaluable for response. Overall response rate was 78% (29/37, 95% confidence interval [CI] 62%-90%), including four (11%, 95% CI 3%-25%) complete and 25 (68%) partial responses. Objective tumor response correlated with degree of HER2 positivity: immunohistochemistry (IHC) 3(+) = 82% (18/22) response and IHC 2(+) = 58% (7/12) response. Median time to progression was 72 weeks (95% CI 37-138 weeks); median survival has not been reached. Grade 3/4 neutropenia was the most frequent serious toxicity and cause of dose reductions (9% of courses) and omissions (10% of courses). No patient experienced serious cardiac toxicity.
Conclusions: Weekly vinorelbine/trastuzumab offers a high therapeutic index as initial therapy in patients with HER2(+) metastatic breast cancer. Further investigation of this novel regimen is planned.