MRC1 and neoplasm: Microsatellite instability is defined as small deletions or expansions within short tandem repeats in tumour DNA, which resulted from the inactivation of the DNA mismatch repair (MMR) system and characterised by the absence of protein expression encoded by the corresponding MMR genes (hMLH1, hMSH2, hMSH6 or PMS2) [97–100].