Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant cancer predisposition syndrome associated with a high risk for colorectal cancer (up to 80%), endometrial cancer (up to 60%), and increased risk for other malignancies, mostly ovarian and urinary system tumors. HNPCC is caused by a germline mutation in one of the mismatch repair (MMR) genes, mainly hMLH1, hMSH2 and hMSH6. The tumors present with microsatellite instability (MSI) associated with loss of heterozygosity of the affected gene, and with loss of expression of the gene product. Diagnosis of HNPCC involves tumor testing for MSI, immunohistochemistry staining and germ line mutation analysis of the suspected gene. Proper genetic counseling is based on the synthesis of the clinical, pathological and molecular data. Directed surveillance shows significant reduction in colon cancer incidence, cancer mortality and overall mortality among HNPCC patients.To establish a multidisciplinary service for patients suspected of having HNPCC.We have established a service which is based on tight collaboration between clinical departments and laboratories. The clinical work-up was conducted by a special oncogenetic clinic and the laboratory service consisted of tissue testing for MSI and immunohistochemistry, denaturing high performance liquid chromatography (DHPLC) for suspected genes, and mutation testing.The efficiency of detection of patients with HNPCC was high, completed in a multistep process. In the first year of our collaborative work, we have provided genetic counseling to over 100 families and performed suitable tests for 46 families. Among them we have identified more than 16 families with HNPCC; 4 showed absence of hMLH1, 1 showed absence of hMSH6, and 11 showed absence of hMSH2. All tumors that showed MSI also showed absence of either one of the three MMR proteins. We present the clinical, pathological and molecular features of our patients and discuss the implication of this data on future recommendations.
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