ESR1 and neoplasm: Several genes involved in cell cycle regulation and apoptosis (CCND2, CDKN2A/p16, RASSF1A), DNA damage response (BRCA1), cell adhesion (CDH1) and cell signaling (ER, RARβ 2) have been reported to undergo promoter hypermethylation in breast carcinoma as well as in other tumor types [6-10].