The effect of estrogen metabolites, 2-OHE2 and 4-OHE2, on the growth of MCF-7 breast cancer cells. a 2-OHE2 (black bars) and 4-OHE2 (gray striped bars) were titrated from 10−9 to 10−6 M. A vehicle control, ethanol (white bar), is shown on the left. b The anti-estrogen, ICI 182,780 (fulvestrant), blocked 2-OHE2- and 4-OHE2-stimulated growth. MCF-7 cells were grown as indicated in the figure and the concentrations of anti-estrogen, estrogen, and metabolites used were ICI at 10−8 M, E2 10−10 M, and 2-OHE2 and 4-OHE2 at 10−7 M. c MCF-7 cells were treated with increasing concentrations of TMS and then either 10−10 M E2 (black circles), 10−10 M E2 + 10−7 M 4-OHE2 (open circles) or 10−10 M E2 + 10−7 M 4-OHE2 + 10−7 M 2-OHE2 (black triangles) were added back to the TMS-treated cells