RARB and breast cancer: For example, RASSF1A, CDH13 and RARβ have been reported to be frequently methylated in breast cancer (average frequency of 71 %, 49 % and 21 % respectively, Additional file 1: Table S1), which is similar to our results of 64 %, 51 % and 19 % methylation in both ipsilateral and contralateral pairs respectively.