Selenium inhibition of N-methyl-N-nitrosourea-induced mammary carcinogenesis in the rat.

The effect of supplemental dietary selenium on the postinitiation state of N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis was investigated in noninbred female Sprague-Dawley rats. Mammary cancer was induced by a single iv injection of MNU. Supplemental selenium feeding was begun 7 days after carcinogen treatment. Feeding of selenium prolonged the latency of mammary cancer appearance and resulted in a reduction in the average number of cancers per rat. The results suggested an inhibitory effect of pharmacologic levels of dietary selenium on the postinitiation stage of mammary carcinogenesis.