MSH2 and MLH1 immunodetection and the prognosis of colon cancer.

MSH2 and MLH1 are proteins involved in DNA reparation. They are mutated in some forms of colon cancer, i.e. hereditary non-polyposis carcinomas and a subset of sporadic carcinomas. We have studied the expression of MSH2 and MLH1 in a retrospective series of 225 colorectal carcinomas by immunohistochemistry. The results were compared to molecular tests of microsatellite instability using amplification by PCR of BAT-25 and BAT-26 repeated sequences and to histoclinical data. Positivity of both proteins was never associated with MSI phenotype. MSH2 and/or MLH1 negative tumors were frequently tumors of the proximal colon; in this subpopulation or proximal tumors, MSH2 and/or MLH1 negativity was associated with a longer disease-free survival.