Lack of selective killing by steroids in normal and malignant cells.

Using a colony formation assay, the cytotoxic effects of steroids and an anti-steroid on an established human breast tumor line and two human diploid fibroblast strains were studied. Experiments involving 17 a-estradiol, 17 beta-estradiol, dexamethasone, cortisone, dihydrotestosterone, and the anti-estrogen Tamoxifen showed no killing at concentrations below 10(-7)M following a 24-hour exposure to these agents. A maximum of 80% killing was observed at 10(-5)M with dexamethasone in one fibroblast strain and at the same dose of 17 beta-estradiol in the breast tumor line. The extent of killing observed is insufficient to account for many of the clinical remissions observed with steroid therapy. The data also suggest that at therapeutic doses, there is no selective killing of malignant cells by these agents.