Estramustine binding site in human breast cancer biopsy samples. Its relation to estrogen and progesterone receptor levels, age and menopausal status.

Estramustine is a cytotoxic metabolite of estramustine phosphate (Estracyt), which is used in the treatment of prostatic carcinoma. An estramustine binding site (EMBS) at pH 4.8-4.9 was demonstrated in 74 of 306 (24%) breast cancer biopsy samples using isoelectric focusing in polyacrylamide gels. The presence of EMBS was significantly (P less than 0.001) correlated with negative or low estrogen and progesterone receptor values. EMBS positivity was found in 31% of the samples from pre- and perimenopausal patients and in 22% of the samples from postmenopausals. If patients were instead divided into different age groups, EMBS positivity was most frequent in samples from patients between 50 and 59 years of age (42%). With increasing age the percentage of EMBS positivity fell successively. For patients under 50 years, no difference with respect to EMBS positivity between age groups could be demonstrated. The possible value of EMBS determinations in breast cancer tissue specimens for the selection of those patients that will respond to Estracyt therapy should be evaluated.