Relationship of cyclic AMP binding capacity and estrogen receptor to hormone sensitivity in human breast cancer.

Estrogen receptor (ER) and total binding capacity for cyclic AMP (cAR) were measured in cytosols from human mammary tumors. Patients with advanced, evaluable breast cancer were biopsied before the start of endocrine treatment, and ER and cAR measurements were performed. All patients included in this study were ER positive. Sixteen of 30 patients (53%) had an objective response to endocrine treatment. When ER and cAR were expressed as a ratio and this ratio was related to treatment response, it was found that all objective responders had ratio values above 2.5 X 10(-3). Nine of 14 nonresponders had ER/cAR ratios below this value. In our limited series of patients a threshold limit of 2.5 X 10(-3) would have correctly predicted the response to endocrine treatment in 25 of 30 patients (83%). In patients with ER values below 100 fmol/mg protein and PgR negative or unknown, cAR might strengthen the predictive value of steroid receptor measurements.