Progesterone and progesterone receptors in experimental breast cancer.

in ER-positive tumors would indicate that the tumor is capa ble of synthesizing at least 1 end product under estrogen regulation and may therefore be endocrine responsive (8). Although the hypothesis assumes that PGR levels in breast tumors, like those in the uterus, are under estrogen control, this priming effect has never been demonstrated. In this paper we show that PGR in the DMBA-induced mat mam manytumor is under acute estrogen control and that PGR is rapidly depleted in tumors regressing after estrogen with drawal.