Induction of mammary cancer in CD rats fed bracken diet.

Fifteen male and 15 female Charles River Sprague-Dawley rats (CD rats) of 6 weeks old were given a diet containing 30% bracken fronds throughout the experimental period of 260 days. Male rats fed bracken diet developed multiple ileal tumors and urinary bladder tumors with incidences of 100% and 60%, respectively. Female rats developed multiple mammary tumors with an incidence of 87% in addition to ileal and urinary bladder tumors. The earliest mammary tumor was detected on day 78, and the last on day 256. The average number of tumors per rat was 5.6. Most mammary tumors were papillary carcinomas and adenocarcinomas. No tumors were found in rats in the control group.