Phase II trial of doxorubicin and trifluoperazine in metastatic breast cancer.

Pre-clinical and clinical studies have shown that trifluoperazine (TFP) can modulate multidrug resistance. We have performed a Phase II trial of TFP and doxorubicin in doxorubicin-naive patients with metastatic breast cancer. We hypothesized that TFP would inhibit the development of doxorubicin resistance, resulting in an increased rate of complete response or a prolongation in response duration. Twenty patients with metastatic breast cancer were treated every 3 weeks with TFP 5 mg by mouth every 6 hours on days 0-5 and doxorubicin 60 mg/m2/96 hr on days 1-4 by continuous intravenous infusion. The first 5 patients were treated with TFP 15 mg by mouth every 6 hours, but the dose was reduced to 5 mg every 6 hours when grade 3-4 extrapyramidal toxicity was noted in 3 of the first 5 patients. Thereafter, neurologic toxicity was grade 0-2. No complete and 9 partial responses were produced in 20 patients (45%). The median response duration was 17 weeks (range 7-112). The combination of trifluoperazine and doxorubicin did not seem to produce a response rate or duration markedly different than that expected for doxorubicin alone in patients with metastatic breast cancer. Alternative trial designs may be necessary in future clinical trials investigating the inhibition of acquisition of drug resistance.