By Prof. CHARLES HUGGINS, LORRAINE C.

GRAND and FILOMENA P. BRILLANTES

Ben May Laboratory for Cancer Research, University of Chicago

One of the most remarkable experiments in cancer research is the induction of cancer which occurs preferentially in the breast of rats following the feeding of carcinogenic hydrocarbons. The first compound found to incite mammary cancer by this method was 2-acetylaminofluorene (2-AAF) which was incorporated in a diet that was fed to rats for many months1. The repeated daily administration of 3-methylcholanthrene (3-MC) to young adult female rats of a special strain induced mammary cancer invariably and rapidly*.3 ; the earliest cancer of the breast was detected by palpation 20 days after beginning the feeding, and within two months every animal had developed multiple tumours of this sort. A newly recognized property2 of the mammary cancers induced by this method was the dependence of many of the tumours on the presence of hormones, since regression takes place after ovariectomy or certain other endocrine procedures. This is a characteristic that is commonly observed in cancer of the breast in human beings, but which is unique among mammary cancers available in the laboratory.

It will now be shown that a single feeding of poly-nuclear hydrocarbons to rats caused selective injuries in the recipient rather than total body damage. These lesions include the induction of leukopenia and of cancers of two types, carcinoma of the breast and of the external acoustic duct. Further, established mammary cancers were suppressed in many rats by treatment with certain hormones or by pregnancy.

The induction of mammary cancer following the application of aromatic carcinogens remotely from the breast was first observed by Maisin and Coolen4 who painted the skin of mice with 3-MC and observed a high incidence of cancer of the breast in addition to cancer of the skin. A single intramuscular injection of carcinogenic hydrocarbons is a classical method of evoking sarcoma in susceptible rodents5. An injection of 3-MC into the breast of mice gave rise to sarcoma and adeno- and squamous carcinoma of the mammary glands6. A single intravenous doso of urothane gave rise to benign pulmonary tumours in mice'.