Proliferation and apoptosis in human breast explants. Proliferation in human breast explants (n = 9) at various time points and treatment groups was determined by Ki-67 and PCNA, and apoptosis by FragEL™. Comparison of expression of Ki-67 positive cells in explants cultured for 7 days (A-acini, B-duct) with explants cultured for 14 days (C-acini, D-duct) in vitro with E2. Note that cell proliferation was increased after 14 days (p < 0.001). Examples of expression of PCNA in E2 treatment groups after 7 (F-acini, G-duct) and 14 days of culture (H-acini, I-duct). Note that intensity of PCNA staining diminished after 14 days when compared with staining intensity after 7 days of culture. Cell apoptosis in cultured explants after 21 days: (K)-control group; (L)-10 nM E2 group; (M)-100 nM MPA; (N)-10 nM E2 and 100 nM MPA group. The number of apoptotic cells decreased in all hormone treatment groups compared with control at 7, 14 and 21 days in vitro. Proliferation (Ki67, a, and PCNA, b) and apoptosis ratios (FragEL™, c). Proliferation and apoptosis indices were counted per 1000 epithelial cells at days 7, 14 and 21 of organ culture with different hormonal treatments. Columns represent the mean counts ± SD. Asterisks show the statistical significance of differences between control and hormonal treatment groups (*, p < 0.05}; **, p < 0.01}; ***, p < 0.001), NS not significant.