Tumor induction in C57BL-6 mice by a single administration of cycasin.

The incidence and localization of tumors in newborn and adult mice of the C57BL/6 strain that received cycasin were compared with similar groups of rats on which results were previously reported. In the present report the newborn mice received single subcutaneous injections of 0.5 mg cycasin/gm body weight within 24 hours after birth. Each adult animal received one dose of 0 .3-1 .0 mg cycasin/gm body weight through a stomach tube. Tumor incidence caused by cycasin was lower in mice, whether newborn or adult, than in rats. Newborn mice, however, were more susceptible to the carcinogenic effects of cycasin than the adult mice, and the newborn animals developed reticulum cell neoplasms much sooner than the control group. Tumors of the intestine or kidney, frequently observed in cycasin-treated rats, were rarely found in mice. On the other hand, hepatomas, which were extremely rare in rats treated with cycasin, were encountered at a high incidence in mice. All of the newborn mice that survived for more than 280 days after the administration of cycasin developed hepatomas.