Two groups of DNA methylation markers to classify colorectal cancer into three epigenotypes

A subgroup of colorectal cancer (CRC) shows non‐random accumulation of aberrant DNA methylation, so‐called CpG island methylator phenotype (CIMP), which was associated with microsatellite instability and BRAF mutation. As just one group of methylation markers was suitable to extract CIMP+/CIMP‐high, and had been commonly used in the “one‐panel method”, it had been unclear whether another cluster of CRC with DNA methylation accumulation exists in microsatellite‐stable CRC. We therefore epigenotyped CRC by a comprehensive approach, that is, the two‐way unsupervised hierarchical clustering method using highly quantitative methylation data by a single detection method, MALDI‐TOF mass spectrometry, on novel regions selected genome‐widely through methylated DNA immunoprecipitation on array analysis. CRC was clearly clustered into three DNA methylation epigenotypes, high‐, intermediate‐ and low‐methylation epigenotypes (HME, IME, and LME, respectively). Methylation markers are clustered into two distinct groups: Group‐1 methylated specifically in HME and including most reported CIMP‐related markers; and Group‐2 methylated both in HME and IME. While suitable markers to detect a subgroup of CRC with intermediate methylation and correlation to KRAS mutation have been expected to be developed, our data indicated that a “two‐panel method” is necessary to properly classify CRC into three epigenotypes, the first panel to extract HME using Group‐1 markers, and the second panel to divide the remaining into IME and LME using Group‐2 markers. Here we review and compare our recent study and reported CRC classification methods by DNA methylation information, and propose the use of two panels of methylation markers as CRC classifiers. (Cancer Sci 2011; 102: 18–24)