Immunohistochemical Analysis of Mismatch Repair Proteins in Iranian Colorectal Cancer Patients at Risk for Lynch Syndrome

BACKGROUND Hereditary non-polyposis colorectal cancer (HNPCC) is a common hereditary cancer predisposing syndrome has molecular and clinicopathological features still have remained ambiguous within Iranian populations. We discuss in this article some molecular and clinicopathological features of the condition. METHODS The study was a descriptive retrospective and designed on 1659 colorectal cancer (CRC) patients were screened based on early-onset disease and Amsterdam II criteria during 14 years (2000-2013). Immunohistochemistry (IHC) staining was set up to detect expression of mismatch repair (MMR) genes on paraffin-embedded tissue sections of 31 HNPCC-CRC tumors. SPSS 19 software was used to analyze the data. RESULTS IHC-MMR staining was absent in 7/31 individuals (22.6%) of which 4 cases showed IHC-Absent (IHC-A) in both MSH2 and MSH6 (57.1%), in 2 cases both MLH1 and PMS2 had negative staining (28.6%), and just in one case, MSH6 was defective (14.3%). The frequency of CRC among IHC-A and IHC-Present (IHC-P) families was 67.5% and 27.9%, respectively. Also the most frequent extracolonic cancers in IHC-A group were: stomach (10%), small bowel (5%), and prostate (5%); and in IHC-P group: stomach (18.4%), lung (10.9%), and breast (7.5%). Average age of IHC-A individuals at diagnosis was 38.0 versus 45.3 years in IHC-P individuals. Overall, 20.8% and 57.1% of our index CRCs were localized proximal to the splenic flexure in IHC-P and IHC-A groups, respectively. CONCLUSION Given the lack of enough information about molecular aspects of hereditary cancer syndromes like HNPCC in Iran, more evaluations are necessary on larger samples using complementary techniques such as MSI-testing and mutation analyses.