Hormone therapy effects on gene markers related to mammary gland proliferation. (a) markers included cell proliferation (MKI67) and epithelial density (KRT19) and genes involved in the following signaling pathways; (b) STAT5; (c) EGFR; and (d) TGF-beta. mRNA levels were determined by quantitative PCR. Vertical lines indicate 90% confidence interval. Letters indicate significant differences compared with control (P < 0.05a, P < 0.01b, P < 0.001c) and conjugated equine estrogens plus medroxyprogesterone acetate (CEE + MPA), (P < 0.01d, P < 0.001e) groups.