p,p'-DDE increases the proliferation of MCF7-AR1 cells in the presence of 17β-estradiol (E2) and dihydrotestosterone (DHT) (a) or when added alone to the cell culture medium (b). Cell proliferation was assessed after 6 days of treatment. Each bar represents the mean ± standard error of the mean of four independent experiments. A single asterisk indicates P < 0.05 versus E2+DHT treatment and ††† indicates P < 0.001 versus 0.1 μM p,p'-DDE as determined by an analysis of variance followed by a one-tail Bonferroni post hoc test. p,p'-DDE, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene.