It is not known how many sporadic MSI tumours are that caused by MLH1 hypermethylation, but based on the expression levels of MLH1 and reports from the literature a realistic estimate would be 80–90% (Kane et al, 1997; Cunningham et al, 1998b; Herman et al, 1998; Kuismanen et al, 2000). This evidence concerns the gene MLH1 and neoplasm.