Although Myc expression alone is not sufficient to develop malignant breast tumors (Stewart et al., 1984, Tseng et al., 2014), given that Myc overexpression induces a replicative stress and stress-associated diseases, including cancer (Murga et al., 2011), E2-induced MYC expression may be an early event in breast tumorigenesis. This evidence concerns the gene MYC and breast cancer.