Selenium

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2708693/

Selenium – cancer specific cytotoxicity

The selenium salt selenite (SeO32−) is cytotoxic in low to moderate concentrations, with a remarkable specificity for cancer cells resistant to conventional chemotherapy. Our data show that selenium uptake and accumulation, rather than intracellular events, are crucial to the specific selenite cytotoxicity observed in resistant cancer cells

Drug-resistant tumor cells have been shown to be particularly sensitive to selenite toxicity, with growth-inhibiting effects observed at low concentrations harmless to cell type– or patient-matched normal cells