A pilot phase II trial of valspodar modulation of multidrug resistance to paclitaxel in the treatment of metastatic carcinoma of the breast (E1195): a trial of the Eastern Cooperative Oncology Group.

Background: To assess the activity and toxicity of valspodar (PSC-833) in combination with paclitaxel in women with anthracycline refractory, metastatic breast cancer.

Patients And Methods: Limited, multi-institutional, Phase II trial of valspodar at 5 mg/kg/dose orally every 6 hours for 12 doses in combination with paclitaxel 70 mg/m2 administered intravenously as a 3-hour infusion beginning 4 hours after the fifth dose of valspodar, every 3 weeks. Eligible patients had bi-dimensionally measurable metastatic carcinoma of the breast, prior anthracycline therapy or a medical contraindication to anthracycline therapy, no more than one prior chemotherapy for recurrent or metastatic breast cancer, and adequate organ function. Treatment was continued until disease progression or unacceptable toxicity.

Results: Thirty-four patients are evaluable for response and 37 for toxicity. Two (6 percent) patients achieved a complete response and 5 (15 percent) a partial response for an objective response rate of 21 percent (95 percent confidence interval of 9 to 38 percent). Median duration of response was 9.7 months (95 percent confidence interval 8.0-17.2 months), median time to progression was 3.3 months (95 percent confidence interval 2.0-4.2 months), and median survival was 12 months (95 percent confidence interval 8.1-17.3 months). The toxicity experienced was acceptable.

Conclusions: Combination valspodar plus paclitaxel is an active regimen and has acceptable toxicity. The combination is not clearly more active than single agent paclitaxel.