Representative photomicrographs of secondary tumors derived from sorted luminal and basal subpopulations demonstrating similar morphology, ERα expression and heterogeneity of the parent tumor. (A)H&E, (B) ERα IHC, and (C) flow cytometric analysis (Tumor 1: N=3, mean±S.D.; Tumor 2: N=1; others were too small for analysis). Scale bars, 50 μm.