A, PEITC inhibits the proliferation of ER-negative breast cancer MDA-MB-231 and SK-BR-3 cells. MDA-MB-231 and SK-BR-3 cells in estrogen free medium were treated with vehicle, 1, 2.5, 5, or 10µM of PEITC or ICI 182, 780 for 6 days and then counted with a hemocytometer. Experiments were repeated three times, and the means ± SE are shown. B, PEITC reduces the steady state levels of ER-α36 protein in MDA-MB-231 and SK-BR-3 cells. MDA-MB-231 and SK-BR-3 cells were treated with vehicle (DMSO), 1, 2.5, 5, and 10µM of PEITC or ICI 182780 for 12 hours and lysed for Western blot analysis with anti-ER-α36 and anti-β-actin antibodies. Experiments were repeated three times, and the representative results are shown.