Effect of estramustine phosphate on plasma testosterone during treatment of carcinoma of prostate

Estramustine phosphate administered orally at 900 mg. daily depressed plasma testosterone levels in 10 consecutive patients who had previously been treated with estrogen hormones and/or orchiectomy and who were all in relapse from carcinoma of the prostate. Approximately one half of the patients responded to the treatment clinically. The decrease in plasma testosterone did not correlate with the clinical response. The clinical effect of estramustine phosphate may be due to decreased plasma testosterone levels, inhibiton of 5-alpha reductase activity, and a local cytotoxic effect.