Effect of Consumption of Selenium-Enriched Milk Proteins on Human Mammary Tumor Progression

Selenium, an essential trace mineral that becomes anticarcinogenic at supranutritional levels, is readily incorporated into milk proteins when cows are fed high levels of selenium. The objective of this study was to investigate the effects of selenized milk protein on human mammary tumor progression. Four isonitrogenous diets with Se levels of 0.16, 0.51, 0.85 and 1.15 ppm were formulated by mixing low- and high-selenium milk protein isolates with a rodent premix. MCF-7 human breast cancer cells were inoculated into the mammary fat pad of female BALB/c nude mice implanted with slow-release 17 β-estradiol pellets. Mice with palpable tumors were randomly assigned to one of four diets for 10 weeks. Increasing Se intake reduced final tumor volume and the number of tumors > 500 mm3 in volume. There was a two-fold higher proportion of apoptotic cells in tumors exposed to the highest Se level.