Effect of age and sex on the development of neoplasms in wistar rats receiving a single intragastric instillation of 7,12‐dimethylbenz(a)anthracene

Wistar rats of different age and sex received a single intragastric instillation of 7,12-dimethylbenz(a)anthracene (DMBA). During the following 16 months, 136 of 284 rats developed 182 tumors, of which half were malignant. Among 98 untreated controls, 8 rats developed tumors, of which 4 were malignant. Among the youngest groups (8–15 days) exposed to DMBA, fibroadenoma of the breast in females and subcutaneous sarcoma in both sexes were the most frequent. Among young adult females (6–8 weeks), mammary carcinoma predominated; older females (26 weeks) had less breast tumors. Among adult males, epidermoid carcinoma and papilloma of the skin were most frequent. Castration suppressed development of breast cancer.