CDKN2A and ductal breast carcinoma in situ: Significant differences in methylation levels between the DCIS and invasive stage II tumors were observed for six genes RASSF1A, CDKN2A, MGMT, ABCB1, GSTP1 and FOXC1 (p = 0.008, p = 0.005, p = 0.003, p = 0.006, p = 0.010, p = 0.010 respectively).