Results of an immunohistochemistry-based universal screening strategy for Lynch syndrome in patients with colorectal cancer treated in a public hospital from Latin-America

Background There is limited evidence regarding the implementation of an immunohistochemistry-based universal screening for Lynch Syndrome (LS) in Latin America. The aim of this study was to evaluate the results of a universal screening strategy in colorectal cancer in a public hospital from Latin-America. Methods Single center prospective study including patients who underwent colorectal resection for CRC between March 1, 2016 and March 1, 2017. Mismatch Repair status (MMR) based on immunohistochemistry (IHC) was obtained. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for revised Bethesda and modified Amsterdam II criteria. Kaplan-Meier analysis was performed for overall and relapse free survival. Results 65 patients were enrolled (35 women). Median age 58 years (22-88). Main tumor location was left colon (48%). Nineteen patients (29%) had positive Bethesda Criteria. Eight patients (12%) with MMR deficiency were detected by IHC: 5 MLH1/PMS2, 2 MSH2/MSH6 and 1 MSH6. The sensibility and specificity for Bethesda Criteria to assess MMR loss were 50% and 73.8%, respectively. Among the patients with MLH1 loss, one patient had a mutated BRAF and two MLH1 promoter hypermethylation. Of the five eligible patients for genetic study, one did not present mutations, three corresponded to a variable of uncertain significance and one had a pathogenic variant of MSH2. The 5-year overall survival was 63.1% without any difference according MMR status. Conclusions Despite the barriers in public health from Latin America, higher detection rates of patients who should undergo germline sequence study for LS supports the implementation of a universal LS screening strategy.