Tamoxifen can induce slight short-term apoptotic activity in mammary epithelial cells. (A) CC3 immunostained sections of mammary glands from oil- and tamoxifen-treated mice at selected time points. Arrows indicate CC3-positive cells. (B) Bar charts depicting the number of CC3+ cells per pair of oil- and tamoxifen-treated glands analyzed at 1, 2, 3, 7, and 21 days after treatment. (*P < 0.05; **P < 0.01; ***P < 0.0001).