Prevalence and clinicopathological characteristics of mismatch repair-deficient colorectal carcinoma in early onset cases as compared with late-onset cases: a retrospective cross-sectional study in Northeastern Iran.

OBJECTIVES: Lynch syndrome (LS), a genetically inherited autosomal disorder, increases the incidence of colorectal carcinoma (CRC). We aimed to perform a universal strategy to assess the prevalence and clinicopathological characteristics of early onset CRCs at high risk of LS versus late-onset ones in the Iranian population. SETTING: A local population-based study from Northeastern Iran. PARTICIPANTS: 321 consecutive CRCs and pathology specimen screened between 2013 and 2016. PRIMARY AND SECONDARY OUTCOME MEASURES: Retrospectively, information regarding the clinical criteria was obtained by interviewing the patients with CRC or, their families. Pathologists tested tumours with immunohistochemistry (IHC) staining of four mismatch repair (MMR) proteins (MLH1, MSH2, MSH6 and PMS2). Tumours with absent IHC staining of MLH1 were tested for BRAF mutations to exclude sporadic CRCs. Prevalence of early onset CRCs at high risk of LS and familial CRC type X were assessed as primary and secondary outcome measures, respectively. RESULTS: Of 321 CRCs (13/123 (10.57%), early onset vs 21/198 (10.6%) late-onset) were detected to be MMR-deficient (dMMR). Nine early onset cases and 14 late-onset ones with a loss of MLH1 underwent testing for the BRAF mutation, none of the early onset and four (2.02%) late-onset were recognised as sporadic. The difference in the outcome of IHC-analysis between early and late-onset CRCs at high risk of LS was not statistically significant (p=0.34). Majority of the suspected LS tumours from early onset patients had arisen in distal part (8/11 (72.72%) vs 8/14 (57.14%)), all of which were occurred in the rectum or sigmoid. CONCLUSION: Clinically, these findings suggest that in case of limitation for BRAF testing, the practitioner in Iran may consider managing early onset dMMR cases like LS until access to BRAF testing becomes available to them, before germline testing to accurately diagnose LS.

Screening for Lynch Syndrome in Cases with Colorectal Carcinoma from Mashhad.

INTRODUCTION: Lynch Syndrome (LS) is a genetically inherited autosomal disorder that increases the risk of many types of cancer, especially colorectal cancer (CRC). Identifying these subjects improves morbidity and mortality. We aimed to assess the prevalence of LS with both clinical criteria and universal strategy in Mashhad, Iran. METHODS: In this retrospective study, we screened 322 patients with CRC between 2013 and 2016 in Mashhad, Iran. CRCs were screened based on Amsterdam II criteria, revised Bethesda guideline, and universal strategy. Information regarding the clinical criteria was obtained by interviewing the patients or, their families. Tumors were screened by pathologists with IHC staining of four Mismatch repair (MMR) proteins (MLH1, MSH2, MSH6, and PMS2). Tumors with absent IHC staining of MLH1 were tested for BRAF mutations to exclude sporadic CRCs. RESULTS: Of 322 CRCs, 33 cases were found to be deficient-MMR; 22 of these had concurrent loss of MLH1 and PMS2, followed by concurrent loss of MSH2 and MSH6 in 8 CRCs. Twenty-two cases with a loss of MLH1 underwent testing for the BRAF mutation, 4 of which were recognized as a positive BRAF mutation. Finally, 29 CRCs were found as being positive screen for LS. Poor sensitivity (21.74%) was found for the Amsterdam II criteria and a poor positive predictive value (15.39%) for the revised Bethesda. CONCLUSION: Application of clinical criteria may not be effective enough to identify LS and at least 2-antibody panel (PMS2, MSH6) should be conducted for newly diagnosed CRCs.