ESR1 and cancer: Some of the genetic causes which contribute to cancer progression are the high-penetrance genes (BRCA1, BRCA2, p53, PTEN, ATM, NBS1, and LKB1) (2), cytochrome P450 genes which are low penetrants (CYP1A1, CYP2D6, and CYP19) (3), genes of glutathione S-transferase family (GSTM1 and GSTP1) (4, 5), alcohol and one-carbon metabolism genes (ADH1C and MTHFR) (6), genes involved in DNA repair (XRCC1, XRCC3, and ERCC4/XPF) (7), and cell signaling molecule encoding genes [PR, ER, TNF-α, or heat shock protein 70 (HSP70)] (8, 9).