REV1 and breast cancer: Moreover, the majority of SNPs associated with risk of breast cancer are present in the following genes: mitogen-activated protein kinase kinase kinase 1 (MAP3K1), RAD51 paralog B (RAD51L1), BRCA1, BRCA2, estrogen receptor 1 (ESR1), MDM5, transforming growth factor beta 1 (TGFB1), telomerase reverse transcriptase (TERT), carbohydrate sulfotransferase 9 (CHST9), or REV1 DNA directed polymerase (REV1).