Dehydroepiandrosterone sulfate causes proliferation of estrogen receptor–positive breast cancer cells despite treatment with fulvestrant

HYPOTHESIS: Dehydroepiandrosterone sulfate (DHEA-S) causes a proliferation of estrogen receptor (ER)-positive breast cancer cells, even with tamoxifen citrate blockade. The ER antagonist ICI 182780 (fulvestrant) will more effectively stop the proliferative effect of DHEA-S on breast cancer cells. DESIGN: Examination of in vitro breast cancer cell growth in the presence of fulvestrant and DHEA-S. SETTING: Surgical oncology research laboratory. INTERVENTIONS: The ER-positive and ER-negative breast cancer cells were pretreated with fulvestrant and stimulated with 900 microg/dL (22.8 micromol/L) of DHEA-S. MAIN OUTCOME MEASURES: Assays using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, thiazolyl blue, were performed on the third, fifth, and seventh days poststimulation and permitted the calculation of growth percent change. RESULTS: The ER-positive and progesterone receptor-positive cells demonstrated universal proliferation of 107% by day 7 when treated with fulvestrant, regardless of the dose. The ER-negative and progesterone receptor-negative cells demonstrated growth inhibition. CONCLUSIONS: The DHEA-S circumvented fulvestrant inhibition and caused ER-positive breast cancer cell growth.