Fig. 1.

Estrogen increases cancer stem cells in ERα⁺ cell lines. (A) Average percentage of CD44⁺/CD24⁻/ESA⁺ cells in the ERα⁺ cell line MCF7 following 6-d treatment with either 1 nM 17-β-estradiol (E2) or vehicle (EtOH); n = 5 biological replicates. Data are mean ± SEM. (B) MCF7 tumorsphere formation presented as the average number of spheres per 1,000 cells plated ± SEM; n = 3 biological replicates. Representative phase contrast micrographs of MCF7 spheres are shown. (C) Tumor formation of MCF7 cells pretreated with EtOH and DMSO (vehicles), E2, or E2 and PD173074 injected in limiting dilution into ovariectomized mice. *Nonparametric χ² statistic was used to test the expected vs. observed frequencies of tumor formation at limiting dilution with a level of 0.001 (critical value, 10.83). (D) Representative H&E-stained sections of mammary glands injected with EtOH-pretreated or 1 nM estrogen (E2)-pretreated MCF7 cells are shown.