Interactive effects of selenium and cadmium on mammary tumor development and growth in MMTV-infected female mice.  A model study on the roles of cadmium and selenium in human breast cancer. 
Previous studies demonstrated that the age-corrected breast cancer mortalities in different countries are inversely correlated with the per-capita dietary intakes of selenium and directly with the estimated intakes of cadmium, zinc, and chromium, suggesting that the anticarcinogenic properties of selenium are counteracted by these elements.  The tumor-preventative effects of selenium and the converse effects zinc and chromium have already been confirmed experimentally in studies with female inbred C3H mice carrying murine mammary tumor virus (MMTV).  Using the same model of human breast cancer, it is now demonstrated that cadmium abolishes the cancer-protecting effects of selenium.  In addition, cadmium was also found to interact with zinc, copper, and chromium.  At 1.4 ppm in the drinking water, cadmium caused a significant depletion of zinc in vital organs such as the liver, which is held responsible for a delay of the appearance of the mammary tumors by 4 months and their slower growth rates relative to the Cd-unexposed controls.  The results of the present study are relevant to human breast cancer prevention as selenium counteracts the effects of cadmium.