To further determine whether promoter methylation is responsible for reduced CHD5 mRNA expression in breast cancer, we treated MDA-MB-231 and Hs 578T cell lines, both of which had little CHD5 mRNA expression, with the 5-aza-2'-deoxycytidine (5-aza-CdR) demethylating agent (2 and 5 μM) for three days, and examined the effect of 5-aza-CdR on CHD5 expression. Here, CHD5 is linked to breast carcinoma.