CpG island methylator phenotype in colorectal cancers: Comparison of the new and classic CPG island methylator phenotype marker panels

Context. - CpG island methylator phenotype (CIMP) designates a subset of colorectal cancers featuring concordant hypermethylation of multiple promoter CpG islands. Little is known about the clinical outcome or histologic characteristics of CIMP-positive colorectal cancers defined by recently identified CpG island methylator phenotype panels. Objective. - To investigate and compare the molecular and clinicopathologic features of CIMP-positive colorectal cancers defined by classic (p16, hMLH1, MINT1, MINT2, MINT31) and new (CACNA1G, IGF2, NEUROG1, RUNX3, SOCS1) CIMP panels. Design. - We analyzed 130 colorectal cancers for hypermethylation of both panels using methylation-specific polymerase chain reaction. Results. - With at least 2 markers methylated, both classic (39/130; 23.1%) and new (23.1%) CIMP-positive colorectal cancers were significantly associated with proximal tumor location, microsatellite instability, and BRAF mutation (all P values were less than .05). The new panel outperformed the classic panel in detecting these features. With at least 3 markers methylated, new CIMP-positive colorectal cancers (16.9%) were closely associated with proximal tumor location, low frequency of KRAS mutation, and high frequency of BRAF mutation (all P values were less than .05), whereas classic CIMP-positive colorectal cancers (18.5%) were closely associated with proximal tumor location, frequent microsatellite instability, and frequent BRAF mutation (all P values were less than .05). Analyzing a combination of CIMP and microsatellite instability status, CIMP-positive/ microsatellite instability-negative colorectal cancers had the worst clinical outcomes. Conclusions. - Whereas the classic panel outperformed in predicting clinical outcome, the new panel was superior in detecting known clinicopathologic features of CIMP but inferior in prognostication power.