It has been known for some years that certain aromatic hydrocarbons induce mammary tumors in some species of rodents. This paper is concerned with the conditions required for the rapid and invariable induction of mammary cancer in the rat by administering 3-methylcholanthrene v/a the gastro-intestinal tract and with some of the functional characteristics of the tumors which were evoked. During the experiments, a novel observation was made when it was found that the majority of the induced carcinomas of the breast are hormonedependent, since they regress when the supporting internal secretions are removed. Whilst the concept of hormone dependence has been established in human mammary cancer, this property has not been recognized previously in mammary carcinomas of laboratory animals.Tumors develop preferentially in the mammary gland of certain strains of mice and rats following the remote administration of some aromatic compounds; the local application of such carcinogens to the region of the mammary gland is unnecessary for the production of breast tumors. This effect was discovered by Lacassagne (I) who found that the administration of estrone induced mammary cancer in mice of the R I I I strain.But mammary cancer can be evoked by compounds without hormonal activity; amongst these carcinogens are 3-methylcholanthrene (2), 2-acetylaminofluorene (2-AAF) 1 (3, 4), and 7,12-dimethylbenz-a-anthracene (DMBA) ~ (5). This remarkable activity of non-estrogenic carcinogens in inducing cancers of the mammary glands was first observed by Maisin and Coolen (2) who painted the skin of mice with 3-methylcholanthrene and found that, in addition to production of skin cancer, carcinoma of the mammary gland developed in high incidence. Mammary tumors have also been elicited with great frequency after the repeated instillation of 3-methylcholanthrene in the mouth (6), nares (7), or stomach (8) of the mouse or rat. Repeated intravenous injections of DMBA evoked similar tumors (5).

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Aberrant pancreatic tissue is not rarely encountered in man but has seldom been reported in the lower animals. It has been described in a domestic cat, a cynomologus monkey and in dogs. Among the several thousands of rats he examined, Barron found only one instance of aberrant pancreatic tissue which was seen in the duodenal submucosa. The present report is the first description of aberrant pancreatic tissue in the liver of a rat.

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