Mammary tumors of the rat: a review.

Abstract

A review of the pertinent studies on mammary tumors of the rat is presented. The major topics discussed are: 1) origin and characteristics 2) induced mammary tumors 3) whether virus is implicated in rat mammary tumors 4) mammary tumor-host relationship and 5) chemotherapeutic studies. Millar and Noble demonstrated that although small doses of estrogen increased the tumor growth rate larger doses caused a marked depression of growth. Progesterone has been reported to have no effect on tumor growth or to stimulate growth. If .6 mg of alpha-estradiol were added to an iv injection of carcinogenic hydrocarbons there was a higher incidence and earlier appearance of tumors. Diethylstilbestrol caused an increase in the total number of tumors. Treatment with .1 mcg daily of estradiol-17beta produced a normal incidence of tumors in ovariectomized females. A dose of 1 mcg delayed the appearance of tumors. Progesterone at a dose of 4 mg daily accelerated the time of appearance. Continuous administration of estrogen to rats has been followed by a high incidence of mammary tumors. The injection of estrogens or implantation sc as pellets also induces a high incidence of tumors.