Estrogen receptor content and hormone-responsive growth of mouse mammary tumors.

Abstract

Summary Mammary tumors were induced with estrone and progesterone in ovariectomized GR mice. Nearly all of the induced tumors were hormone dependent and remained so for the next few serial transplantations, after which they became first hormone responsive and finally hormone independent. These tumors were grafted into castrated mice that were treated with estrone and progesterone and into castrated mice that did not receive hormones. The tumors elicited in the hormone-treated castrates by hormone-dependent or hormone-responsive grafts had high estrogen receptor levels, but those obtained after grafting with hormone-independent tumors had low estrogen receptor levels. The tumors obtained in hormone-untreated castrates after grafting with hormone-responsive or hormoneindependent tumors had low estrogen receptor contents. All tumors derived from castrated hosts not given hormones were found to be hormone independent and to have low estrogen receptor contents. These results indicate that in this model system only the cells of a tumor graft that are devoid of an estrogen receptor are able to multiply in the absence of estrone and progesterone. The possible bearing of this finding on the loss of hormone responsiveness of mouse mammary tumors during successive transplant generations is discussed.