Increasing the response rate to cytotoxic chemotherapy by endocrine means

Cloned cell lines of human breast cancer can be growth inhibited by tamoxifen and this inhibition can be reversed by estrogen. We wondered whether tamoxifen inhibition of breast cancer followed by estradiol reversal would increase the efficacy of chemotherapy by increasing the fraction of rapidly cycling cells. We describe a clinical trial in which 110 patients were prospectively randomized to chemotherapy consisting of cytoxan 750 mg/m2 and adriamycin 30 mg/m2 on Day 1 plus 5-FU 500 mg/m2 and methotrexate 40 mg/m2 on Day 8 vs the same chemotherapy plus tamoxifen 20 mg/m2 Days 2-6 and premarin 0.625 mg Q 12-H X 3 on Day 7. Chemotherapy was given in 21-day cycles. 108 patients were evaluable. No difference exist for any important prognostic variables. The first 55 patients were randomized to a regimen in which 5-FU preceded methotrexate by 24 h; thereafter, all patients received methotrexate followed in 1 h by 5-FU. No difference in any response parameter was seen between these two 5-FU methotrexate schedules. No differences in percent of protocol chemotherapy administered or observed toxicity was seen between the 2 regimens. Objective response rate was nearly identical--57% without and 64% with additional hormones. Prior adjuvant chemotherapy with L-PAM had no observable effect on response rate, response duration or survival. In a limited number of patients with inflammatory breast cancer we saw a significantly higher response rate (93 vs 61%; P = 0.03) than in patients with recurrent metastatic disease. Time to progression (13 vs 17 months) and survival (17 vs 23 months) of responders significantly favored the treatment arm including tamoxifen and premarin. Greater benefits of additional tamoxifen and premarin were seen in partial vs complete responders. This may have resulted from lower doses of chemotherapy given to patients achieving a complete remission. An additive effect of hormones plus chemotherapy cannot be entirely excluded as the explanation for the improved results seen with the addition of tamoxifen for 4 days plus 1 day of premarin. We believe that our results suggest that further efforts to increase the efficacy of chemotherapy by perturbing tumor growth rates may be worthwhile.