Relationship of hormone dependency to estrogen receptor and adenosine 3',5'-cyclic monophosphate-binding proteins in rat mammary tumors.

Estrogen-binding activity and the binding activity of adenosine 3',5'-cyclic monophosphate (cAMP) were assayed in the cytosol of biopsy specimens from 70 rat mammary tumors. The response of these tumors to host ovariectomy was followed. The hormone dependency of the tumors was closely related to the relative concentrations of estrogen receptor (ER) and cAMP-binding protein (CR) in the tumor cytosol. When ER and CR were expressed as the ER/CR ratio, 36 of 38 (95%) hormone-dependent tumors had ratios of 35 X 10(-3) or more, whereas 31 of 32 (97%) hormone-independent tumors had ratios of less than 35 X 10(-3). When ER alone was measured, hormone dependency could be correctly predicted in only 60% of the tumors because the ER range for individual tumors of both types greatly overlapped. Ratios of ER/CR were also elevated in normal estrogen target tissues as compared to those in normal estrogen nontarget tissues. Thus determination of the ER/CR ratio in tumor cytosols appeared to be a more reliable method of predicting hormone dependency than was determination of ER alone.