PGR and breast cancer: At the individual gene level and compared to controls, ATF3-induced mammary tumors exhibited reduced expression of Rb1, Esr1, and Pgr, and increased expression of Erbb2, Egfr, and the genes encoding keratins 5, 6, and 17 (Figure 1B), which is similar to basal-like human breast cancer tumors [42,43].