With the onset of microarray gene expression profiling of large sets of tumors in the last decades, BC is classified into at least four major molecular subtypes: luminal A and luminal B (both ER and PR positive), human epidermal growth factor receptor 2 positive (HER2+) and basal-like (also called triple-negative breast cancer (TNBC)) [2, 3]. This evidence concerns the gene PGR and breast cancer.