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Daily administration of a brominated triphenylethylene (TBP), to rats which received 20 mg of DMBA p. o. inhibits mammary carcinogenesis. The effect appears even with very small doses (i ppm in the diet) and seems to be dose related. With one exception (an adenofibroma) the tumours in control and treated animals were malignant. Administration of TBP prevents the appearance of corporea lutea in the ovaries but not the usual necrosis of the adrenal cortex.

Administration of a bromotriphenylethylene to C3H/f(XVII/G) female mice implanted with a pituitary under the kidney capsule produces with high doses (200 mg/kg or 20 mg/kg of diet) a strong inhibition of the development of the mammary glands. With a low dose (2 mg/kg) no inhibition was observed. In mice which received the high doses no hyperplastic alveolar nodules were observed. The activity of the compound is more pronounced after 50 days than after 25 days.

In (C3H X RIII) F1 females a disturbed hormonal balance plays the major role for the etiology of mammary carcinomas. Castration early in life delays the appearance of the tumors. In normal females the adrenal secretions do not intervene in carcinogenesis. In forced bred females or in animals with pseudopregnancies, but not in mothers which nursed their offspring the latencies are shortened. After a graft with one male pituitary to a castrated female the latency is the same as in intact animals. Pituitary grafting to castrated males does not change the frequency or the latencies of spontaneous mammary cancers. One mammary cancer was observed in an intact male implanted with a pituitary. It is stated that in our animal model progesterone is not an essential factor for mammary carcinogenesis.

Administration of bromotriphenylethylene to C3H/f female mice implanted with a pituitary under the kidney capsule produce an inhibition of mammary carcinogenesis with high doses (20 ppm or 200 ppm in the diet). With a diet containing 2 ppm no inhibition is observed.

Castrated male (C3H X RIII) F1 mice were treated with graded doses of estradiol-17-beta and estrone in a life-span experiment. Estradiol-17-beta incorporated into paraffin pellets was implanted under the skin for continuous resorption. These pellets contained 1 microgram, 2.5 microgram, 5 microgram, 10 microgram or 100 microgram of hormone. Estron was given orally, mixed with the food at 3 daily dosages: 0.06 microgram, 0.6 microgram and 6 microgram. Although the smallest dosages of both hormones induced vaginal estrus in castrated females, they did not produce mammary tumors. The mammary tumor incidence reached progressively almost 100% in response to the increase of the hormonal dosages. The absence of effect of low doses of estrogen in mice is compared with the absence of an excess of breast cancers among women using oral contraceptives.

The plasma levels of ovarian steroids and the steroid binding capacity in the cytosol of mammary glands have been determined in the low-mammary-tumor C3H/f (XVII) mice. Implantation of a pituitary under the kidney leads to an increase of all these parameters as well as a high mammary tumor incidence. Simultaneous administration of the trans isomer of broparestrol (TBP) leads to a decrease of all the parameters.

The trans isomer of a bromotriphenylethylene (TBP) inhibits spontaneous mammary carcinogenesis in (C3H x RIII)F1 females, which received a diet containing 20 ppm of the chemical: intact, spayed, and spayed and pituitary implanted animals. Mammary carcinogenesis is inhibited even if the administration of the compound starts late in life. TBP has no activity on mammary carcinogenesis of castrated males implanted with an ovary.