Minimal single-agent activity of maytansine in refractory breast cancer: a Southwest Oncology Group study.

Maytansine is an experimental antitumor agent that has shown minimal efficacy against breast cancer with minimal myelosuppression in phase I trials. Forty-one patients with advanced drug-resistant breast cancer were treated with a 5-day intermittent iv infusion of maytansine repeated every 21 days. All patients had been heavily pretreated with cyclophosphamide, methotrexate, 5-fluorouracil, or doxorubicin, and 12 had received vinblastine, mitomycin C, or investigational drugs. All patients had measurable disease and an expected survival of 6 weeks. The average performance status was 2.5. Twelve patients did not complete one full cycle of therapy, leaving 29 evaluable for response. One patient had a partial regression of pulmonary disease, seven had transient responses of less than 50% reduction in tumor or stable disease, and 21 had progressive disease. Toxic effects (vomiting, diarrhea, ileus, lethargy, and altered mentation) were considerable. Since maytansine is a relatively nonmyelotoxic metaphase inhibitor, we feel that even minimal efficacy in heavily pretreated patients justifies further evaluation of the agent in combination therapy.