ESR1 and breast cancer: FOXC1, a transcription factor active in myoepithelial cells,21 was significantly upregulated (FC = 1.33; 95% CI, 0.62 to 2.03; P < .001) (Figure 5B), and FOXA1, involved in mammary gland differentiation and modulation of ER and AR functions in breast cancer,22 was significantly downregulated (FC = −2.74; 95% CI, −4.24 to −1.23; P < .001) (Figure 5B).