Two promoters are shown to regulate expression of ERβ (0N, 0K) with 0N regulating ERβ1 and 0K regulating ERβ5.52 Published studies suggested that epigenetic but not genetic regulation of ERβ1 especially methylation adjacent to promoter 0N was a key regulatory event for ERβ1 silencing53 and that promoter 0K was normally unmethylated in cancer cells and tissues.54 Since we only observed changes in expression of ERβ1 with HDACi, we examined epigenetic modification at 0N promoter. This evidence concerns the gene ESR2 and cancer.