Selenium-mediated inhibition of mouse mammary tumorigenesis.

The effects of selenium of mouse mammary tumorigenesis were examined in 2 systems. BALB/cfC3H (MuMTV-S positive) given 2 and 6 ppm selenium in the drinking water and maintained as breeding mice, had significantly lower incidences of mammary tumors (48% and 12%, respectively) than untreated control mice (82%). Selenium at 4 ppm inhibited the tumor-producing capabilities of only 1 of 4 preneoplastic outgrowth lines maintained in BALB/c (MuMTV-S negative) mice. Selenium at 2, 4 and 6 ppm had no effect on the growth rate of primary mammary tumors transplanted subcutaneously in BALB/c mice. Selenium inhibited mammary tumorigenesis without interference of normal reproductive function and weight gain.