MCF10A nontumorigenic breast epithelial cells (isolated from the mammary gland of a patient with fibrocystic disease) and MCF7 breast adenocarcinoma cells (estrogen receptor-positive, ER+) were selected for the study of TGFB1 (a key member of the TGFβ superfamily) signaling. This evidence concerns the gene ESR1 and breast fibrocystic disease.