Combined deficiency of hMLH1, hMSH2, hMSH3 and hMSH6 is an independent prognostic factor in colorectal cancer

We examined biological and clinicopathological significance of individual and combined hMLH1, hMSH2, hMSH3 and hMSH6 expression with immunohistochemistry in 301 unselected colorectal cancers. Weak hMLH1 expression was correlated to microsatellite instability (P=0.04), negative p53 expression (P=0.005) and mucinous carcinomas (P=0.02). Weak hMSH2 expression was related to negative ras (P<0.001) and p53 expression (P=0.005), and better survival (P=0.03). hMSH2, hMSH3 and hMSH6, as well as hMLHI, hMSH2, hMSH3 and hMSH6, were combined into a 'functional' and a 'less-functional' group, respectively. Both 'less-functional' groups were/tended to be associated with microsatellite instability, negative ras and p53 expression, and better survival. In summary, hMLHI and hMSH2 were more important when investigated individually, and the combined groups were more related to the mutator pathway, suggesting that combined deficiencies of the proteins are more efficiently involved in the mutator pathway. Our result from weak versus strong staining may suggest that the intensity of staining should be considered in future studies on mismatch repair proteints.