Cell Identity Disruption in Breast Cancer Precursors

Abstract Mammary epithelial cell identity depends on a set of genes epigenetically-regulated by maintenance proteins, the best-characterized of which belong to the Trithorax and Polycomb groups. Perturbations in expression of these proteins may disrupt cell identity and trigger tumor initiation. The pattern of expression of a panel of genes involved in control of cell identity and mammary gland remodeling was investigated in two precancerous lesions, atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS) and compared to the corresponding histologically normal tissue. ADH and DCIS showed a close association in overexpression of Polycomb complex components, silencing of Homeobox A (HOXA) cluster gene, and overexpression of the genes involved in estrogen signaling, specifically, forkhead box A1 (FOXA1) and GATA binding protein 3 (GATA3) pioneer factors, and estrogen receptor-1 (ESR1). Our findings support the hypothesis that disruption of epigenetic control is associated with loss of cell identity and acquisition of a constitutive estrogen-dependent terminally-differentiated luminal phenotype.