Histochemical assay of estrogen and progesterone receptors in breast cancer: correlation with biochemical assays and patients' response to endocrine therapies.

Estrogen (ER) and progesterone (PgR) receptors were assayed by histochemistry in primary, recurrent, and metastatic breast cancer. Ligand-conjugates composed of 17 beta-estradiol and 11 alpha-hydroxyprogesterone covalently linked to bovine serum albumin and labelled with fluorescein isothiocyanate were employed. Results were compared with those of conventional biochemical receptor assays and correlated for ER in 92% of 314 tumors and for PgR in 86% of 86 specimens. ER and PgR determinations by both assay systems were correlated with clinical response to various endocrine therapies in 40 women with Stage IV disease. The histochemical assay enabled successful prediction of response in 80% of cases including eight which could not be fully analyzed biochemically.