MLH1 and colorectal cancer: Therefore, several organizations including the US Multi-Society Task Force on Colorectal Cancer [26], the US National Comprehensive Cancer Network (NCCN) [63] and the UK National Institute for Health and Care Excellence (NICE) [64] have recommended testing all patients with colorectal cancer for Lynch syndrome; the tumor should be tested for mismatch repair by either DNA analysis or immunohistochemistry for MLH1, MSH2, MSH6 and PMS2 proteins.