The influence of sex hormones on mammary tumors induced by 2-acetaminofluorene.

Abstract

The effects of estrogen androgen and progesterone on the development of mammary tumors were investigated in 179 virgin female Sherman and 196 male Wistar rats receiving 0.03% 2-acetaminofluorene in their diet. The rats were divided into control group (57 females and 79 males) endogenous estrogen (17 females) exogenous estrogen (36 females and 52 males) exogenous androgen (32 females and 51 males) and progesterone (26 females and 14 males) groups. The incidence of mammary carcinoma in rats receiving 2-acetaminofluorene was not increased by simultaneous administration of estrogen but was greatly increased by progesterone. Breast tumors not found in carcinogen-treated males occurred in a small percentage receiving estrogen and in 1 receiving testosterone. It is suggested that small amounts of estrogen may be essential for the development of breast cancer in the 2-acetaminofluorene-treated rats but that the limiting hormonal factor may be the quantity of progesterone. Ongoing studies on the effects of simultaneous administration of progesterone and estrogen to males and castrated females receiving 2-acetaminofluorene should determine the validity of this hypothesis.