Prior estrogen therapy as a predictor of response to subsequent estramustine-based therapy in androgen-independent prostate cancer patients

Abstract

4595 Background: Secondary hormonal therapy with estrogens results in PSA responses in 30–60% of androgen-independent prostate cancer (AiPCa) patients. Diethylstilbestrol (DES) and other estrogens share a similar chemical structure with estramustine phosphate, which is commonly used together with taxanes as chemotherapy for AiPCa patients. It is unknown if prior estrogen therapy impacts on subsequent responses to estramustine-based chemotherapy. Methods: A retrospective chart review of 76 consecutive AiPCa patients who received secondary hormonal therapy with estrogens (DES or PC-SPES) was conducted. Patients who went on to receive estramustine-based chemotherapy were identified and their medical records abstracted. PSA response proportions (using Consensus Criteria), duration of response and overall survival was calculated. Results: Between 1998 and 2003, 76 AiPCa patients were treated with an estrogen (DES or PC-SPES). 48/76 (63%) had a PSA response. Of these, 24 subsequently were treated with estramustine-based chemotherapy. All but 1 had failed to respond to estrogen or developed progressive disease while on estrogen. 23/24 (96%) had metastatic disease. Median PSA was 69.1ng/mL. A PSA response to estramustine-based chemotherapy was observed in 13/23 (57%; CI = 34%–77%). Prior response to DES or PC SPES did not predict the likelihood of subsequent response to estramustine-based therapy (63% response rate in prior estrogen responders, 53% response rate in prior estrogen non-responders, p = 0.67). Conclusions: The use of prior estrogen therapy in AiPCa patients does not have an obvious impact on the likelihood of subsequent response to estramustine-based therapy, with 57% of patients responding to estramustine-based therapy following estrogen therapy. Prior response to estrogen was not predictive of response to estramustine-based therapy. These data suggest that estrogen and estramustine have different mechanisms of action, and that prior estrogen therapy need not exclude AiPCa patients from estramustine-based regimens. No significant financial relationships to disclose.