Inhibition of human breast cancer cells by selenium.

The viability of human breast cancer cells (cell lines MCF-7 and MDA-MB 231) was inhibited in vitro in a dose-dependent manner by selenium supplementation. However, a normal diploid human cell line (MRC-5) was relatively resistant to selenium supplementation. The presence of selenium as Na2SeO3 at 1.1 X 10(-6) M reduced cancer cell viability by approximately 50%, whereas non-cancerous cells were not affected. Parenteral administration of sodium selenite also significantly inhibited the growth of the cancerous cell lines transplanted into nude mice. Selenium administration at 0.8 micrograms/g body wt resulted in an 80-93% reduction in the rate of tumor growth without apparent ill effects on the host.