Previous studies found that many promoter regions of genes were heterogeneously methylated, such as GHSR in breast cancer [20], CDKN2B in acute myeloid leukemia [40], DAPK1 and LPL in chronic lymphocytic leukemia [45, 46], RARB [47] and SOX18 [19] in non-small cell lung cancer, and ABO, RUNX3, CDH1, CDH13 in oral tongue squamous cell carcinomas [18]. Here, RARB is linked to breast cancer.