Thirdly, from a genetic perspective, Genetic polymorphisms associated with GDM (e.g., TCF7L2, IRS1) in North American populations (particularly those of European ancestry) (66) may intersect with breast cancer protective pathways (e.g., estrogen metabolism), counteracting the carcinogenic effects of hyperglycemia (2, 17). This evidence concerns the gene TCF7L2 and breast cancer.