The type of pathogenic variants in repetitive sequences is associated with the extent of MSI and predicts clinical presentation, choice of conventional therapy, and outcome: Mononucleotide sequence changes are typically associated with most MSI-H tumours (often MLH1, MSH2, and MSH6 mutated) which are sensitive to 5-fluorodeoxyuracil. This evidence concerns the gene MLH1 and neoplasm.