Moderate-dose vincristine infusion in refractory breast cancer

Continuous infusion of vincristine at the maximally tolerated infusion dosage of 0.5 mg/m2/day for 5 days has been investigated in 15 patients with refractory breast cancer. Infusion courses were repeated every 3 weeks in the absence of disease progression or prohibitive toxicity. Progressive disease was observed in 14 patients. A partial response lasting 2 months occurred in a patient with pulmonary and skin metastases who had previously received vincristine by bolus injection. Toxicity consisted primarily of mild neurotoxicity of similar degree to that expected with bolus injection. Thrombocytopenia occurred, but was uncommon. The cumulative response rate at this dosage level (2/16, 13%) in our phase I-II trials indicates very limited clinical activity of vincristine infusion in advanced, refractory metastatic breast cancer.