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 immunohistoc hemistry. The results were compared to molecular tests of microsatellite in stability using amplification by PCR of BAT-25 and BAT-26 repeated sequence s and to histoclinical data. Positivity of both proteins was never associat ed with MSI phenotype. MSH2 and/or MLH1 negative tumors were frequently tum ors of the proximal colon; in this subpopulation or proximal tumors, MSH2 a nd/or MLH1 negativity was associated with a longer disease-free survival.