MLH1 and neoplasm: Immunohistochemical staining for microsatellite instability (MSI) screening status was performed as previously described, whereby tumours lacking expression of any of the DNA mismatch repair proteins MLH1, PMS2, MSH2 or MSH6 were denoted as having a positive MSI screening status, and tumours expressing all MMR proteins as being microsatellite stable (MSS) [18].