Relationship between proliferative activity and estrogen receptors in breast cancer.

The proliferative activity of breast cancer has been analyzed in relation to the hormonal characteristics of the host and of the tumor for 199 patients. The analyses of labeling index frequency distributions of estrogen receptor positive (ER+) and negative (ER-) cancers from premenopausal and postmenopausal patients have allowed us to identify three different kinetic groups. A first group, with a very low proliferative activity, includes ER+ cancers from postmenopausal patients; a second group, with an intermediate proliferative activity, includes ER+ cancers from premenopausal and ER- cancers from postmenopausal patients; and a third group, with a very high proliferative activity, includes ER- cancers from premenopausal patients. Generally, the amount of estrogen receptors in ER+ cancers is inversely correlated with the proliferative activity. Lower levels of ER in premenopausal in comparison to postmenopausal patients were found in low proliferative activity tumors.