Epigenetic events in normal colonic mucosa surrounding colorectal cancer lesions.

Gene inactivation by promoter hypermethylation has been demonstrated in the colonic mucosa of colorectal cancer (CRC) patients. However, current data do not prove direct involvement of this epigenetic modification in the early stages of CRC. Promoter methylation profiles of E-cadherin, hMLH1, MGMT, p16(INK4a), p15(INK4b) and p14(ARF); mutations of K-ras, B-raf and TP53 and microsatellite instability (MSI) were examined in normal and cancerous colonic mucosal tissue in 82 CRC patients using methylation-specific PCR assays. Methylation of hMLH1 and MGMT in normal mucosa correlated significantly with MSI and K-ras activation in neighbouring cancerous mucosal tissues. Similarly, poorly differentiated tumours were associated with methylated p16(INK4a) and E-cadherin in neighbouring normal colonic tissues (NCTs). Our results indicate that epigenetic changes in mucosa surrounding colorectal neoplastic lesions may describe a 'field cancerisation' phenomenon that may occur previous to genetic alterations in early stages of carcinogenesis.