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Estrogen and Prolactin Receptor Concentrations in Rat Mammary Tumors and Response to Endocrine Ablation¹

The Ben May Laboratory for Cancer Research, The University of Chicago, Chicago, Illinois 60637 [E. R. D.], and Department of Physiology, Michigan State University, East Lansing, Michigan 48823 [G. K., S. M., J. M.]

Estrogen and prolactin receptor concentrations were measured in 24 carcinogen-induced rat mammary tumors and correlated with the tumor response to host ovariectomy or hypophysectomy. It was found that essentially all of the tumors contained some specific estrogen receptor, and all but three contained prolactin receptor. The values for each receptor comprised a continuum from very low to relatively high concentrations, suggesting that previous considerations of hormone dependence on the basis of presence or absence of hormone receptors may be oversimplified. The concentration of each receptor tended to be lower in the hormone-independent than in the hormone-dependent tumors, but there were a number of hormone-independent tumors, but there were a number of hormone-independent tumors with higher receptor levels than some of the hormone-dependent tumors had. A better correlation of tumor response to endocrine ablation resulted from a combination of the 2 receptor levels than from either receptor concentration alone. These results suggest that there is a complex relationship between mammary tumor response to endocrine ablatin and levels of estrogen and prolactin receptors and that some tumors may be dependent upon 1 or both of these hormones for growth.

¹ Supported in part by Contract NO 1-CB-23873, National Cancer Institute (E. R. D.) and in part by NIH Research Grants CA 10771 from the National Cancer Institute and AM 04784 from the Institute for Arthritis and Metabolic Diseases (J. M.).

² Recipient of Research Career Development Award HD 46249 from the National Institute of Child Health and Human Development. To whom requests for reprints should be addressed, at the Ben May Laboratory for Cancer Research, University of Chicago, 950 E. 59th St., Chicago, Ill.

Received 7/18/75. Accepted 10/15/75.