KRAS and colorectal cancer: In these studies, colorectal cancers can be subdivided into five different subtypes based on combinations of tumor markers: type 1 (MSI-H, CIMP+, positive for BRAF mutation and negative for KRAS mutation); type 2 (MSS or MSI-low, CIMP+, positive for BRAF mutation, negative for KRAS mutation); type 3 (MSS or MSI-low, non-CIMP, negative for BRAF mutation, positive for KRAS mutation); type 4 (MSS or MSI-low, non-CIMP, negative for both BRAF and KRAS mutations); and type 5 (MSI-H, non-CIMP, negative for both BRAF and KRAS mutations) [138].