Mammary carcinoma induced by a series of intragastric intubations of 7,12-dimethylbenz[a]anthracene in gonadectomized female and male Sprague-Dawley rats.

Biweekly intragastric intubations of 7,12-dimethylbenz[a]anthracene (DMBA) rapidly induce mammary carcinoma in high yield in gonadectomized female and male rats. These tumors are ovary-independent, though they contain estrogen receptors (ER). In 84.4% of 32 female rats and in 100% of 35 male rats which were gonadectomized at 27 days of age and given 10 mg of DMBA 8 times at 14-day intervals starting from 28 days of age, mammary carcinoma developed 102.4 +/- 28.1 (SD) and 107.2 +/- 25.5 (SD) days, respectively, after the first intubation of DMBA. More than 55% (55 approximately 83%) of seed tumors taken from 18 tumors induced in ovariectomized rats and 18 tumors induced in orchiectomized rats could grow in intact and ovariectomized females and intact and castrated males. Cytosol ER were found in all of 10 tumors induced in gonadectomized male and female rats.