affect mammary gland development, resulting in precancerous and cancerous lesions in adulthood, exert estrogenic effects, activate the expression of genes associated with cell proliferation and BC; associated with EMT and BC progression; activate VEGF associated with angiogenesis, MAPK signaling pathway, Wnt/β-catenin pathway, STAT3 signaling, and DNA repair; induce changes in genes associated with apoptosis and DNA methylation; inactivate p53; increase expression of BRCA1/2, BARD1, CtlP, RAD51, and BRCC3 involved in DNA repair; downregulate PDCD5 and BCL2L11 involved in apoptosis. This evidence concerns the gene STAT3 and breast cancer.