KRAS and adenoma: Four tumor markers have been commonly used to better characterize this heterogeneity: microsatellite instability (MSI), CpG island methylator phenotype (CIMP), somatic mutations in BRAF, and somatic mutations in KRAS. Together, these tumor markers approximate 3 distinct molecular pathways of colorectal carcinogenesis: adenoma-carcinoma (traditional), alternate, and serrated (1, 3, 4).