The Local Induction of Carcinoma of the Mammary Gland by Methylcholanthrene *

In the course of experiments employing methylcholanthrene as a carcinogen after India ink injections, an entirely unexpected occurrence of adenocarcinoma of the mammary gland was encountered in female mice of 2 distinct strains. A similar result occurred without the previous injection of India ink. As the usual result following methylcholanthrene administration subcutaneously is sarcoma, the present observation of adenocarcinoma of mammary tissue is of interest. The data so far obtained are as follows: Male and female mice of seven distinct genetic strains (NH, HE, CBA, C57, JK, CBAN, and N) were injected subcutaneously, when 24 hours or less of age, with 0.05 cc. of Higgins (Wrico) India ink. Two months later, the mice were injected subcutaneously with 1 mg. of methylcholanthrene dissolved in sesame oil. The sexes were not separated. At present, 42 mice have developed tumors at the site of the injection of methylcholanthrene; 16 of these have been in males, 26 in females. All the tumors in the 16 male mice were sarcomas. Eighteen of the tumors in females have also been sarcomas. Eight of the female mice have developed adenocarcinoma of the mammary gland at the site of injection (Figs. 1 to 3). Six of these 8 have been in female mice of the NFL strain; 2 of them have been in female mice of the JK strain. These 8 carcinomas of the mammary gland have been encountered at 82, 104, 163, 173, 184, and 199 days. following the injection of the methylcholanthrene in female mice of the NH strain, and at 203 and 217 days in the female mice of the JK strain. Female mice of both the NH and JK strains kept under the same laboratory conditions as those in the present experiment have an extremely low incidence of spontaneous tumors. In fact, the individuals of the JK strain are considered to be the nearest approach to a resistant-to-cancer strain that has ever been developed by one of