Fasting/refeeding enhances the development of mammary tumors induced by methylnitrosourea in the rat.

The effect of fasting/refeeding on MNU-induced mammary carcinogenesis was investigated. Female Sprague-Dawley rats were given i.p. a single dose of MNU (50 mg/Kg body weight) and beginning 1 week after MNU administration were exposed to 3 cycles of 3 days fasting followed by refeeding (10 days). Rats were palpated twice a week and killed when tumor diameter was about 2 cm. Tumors palpated were registered by location. The exposure to fasting/refeeding after initiation increased the total number of mammary tumors about 2-fold compared to full-fed control group. In addition, fasted rats developed about 3-fold mammary tumors in the cervical-thoracic gland chains versus the abdominal-inguinal gland chains, while no difference in tumor distribution was observed in controls. The present study reports that fasting/refeeding enhances the development of MNU-induced mammary tumors.