Prognostic values of detecting MSI phenotypes in colorectal carcinoma by immunohistochemical method compared to molecular investigation.

BACKGROUND: The identification essentially of hMSH2 and/or hMLH1 alterations has clinical implications for recognition and prognosis of MSI phenotypes cases. In this study, we tried to identify instability by immunohistochemical expression pattern analysis, compared the results with molecular investigation and shown their usefulness as predictive factors for determination of Microsatellite Instability in patients with colorectal carcinomas in routinely. METHODS: Forty seven colorectal cancers and their adjacent colonic mucosa were selected retrospectively for this study. We first studied the potential value of molecular investigation to identify microsatellite instability in which a NCI panel (or Bethesda panel) of five microsatellite was analyzed (Bat-25, Bat-26, D2S123, D5S346 and D17S250). Secondary, we evaluated the immunohistochemical assessment of hMLH1, hMSH2, hMSH6 and PMS2 proteins in tumor and adjacent normal colorectal mucosa tissues. RESULTS: Fourteen cases were scored as MSI and the remaining MSS. Moreover, we found loss of expression for hMLH1, hMSH2, hMSH6 and PMS2 respectively in 9, 10, 6 and 9 of cases. The MSI patients were less than 45 years old, have right localization and mucinous histological type. We found an association between MSH2, age (P=0.03) and staging (P=0.02). MLH1 is associated only with age (P=0.02) while MSH6 with tumor grade (P=0.01). CONCLUSIONS: We found an association between MSI molecular investigation and MMR immunohistochemical expression which may allow one to specifically identify MSI phenotype of patients with colorectal carcinomas. Furthermore, immunohistochemical analysis of MMR protein can be used in routinely for detection of microsatellite instability without occurs to molecular investigation.