COL4A1 and adenoma: It is notable that among 23 genes we found to be methylated in at least 50% of neoplastic samples, 8 were initially identified among genes whose expression was down-regulated in colorectal neoplasia (COL4A1, COL4A2, SDC2, FOXF1, MAFB, EFEMP1, ZSCAN18 and EPB4IL3, Figure 3 and Table 1); the six highlighted in bold are also among the subset with significant down-regulation in adenomas (Additional file 2: Table S1).