Comparison between Next-Generation Sequencing and Immunohistochemistry in the Diagnosis of Lynch Syndrome in Patients with Amsterdam II Clinical Criteria*

Abstract Colorectal cancer (CRC) ranks third as the most incidental in the world. One of its hereditary forms is Lynch syndrome (LS), characterized by mutations in one of the DNA mismatches repairs (MMR) genes (MLH1, MSH2, MSH6, PMS2, or EPCAM). Current protocols suggest screening with clinical criteria followed by immunohistochemistry (IHC) before next-generation sequencing (NGS) for an early diagnosis. However, using IHC as an isolated screening test may interfere with the diagnosis of LS. To assess the correlation between IHC and NGS to diagnose LS in patients who meet the Amsterdam II clinical criteria. Observational study comprising 32 patients of both genders, aged between 20 and 64 years at the time of CRC diagnosis. They must meet the Amsterdam II clinical criteria and be registered in the Hereditary Cancer Program of Hospital de Câncer de Pernambuco (HCP). All patients underwent IHC assessment of malignant tumor and blood sample NGS. The NGS yielded 11 (34%) positive results for LS. There was a correlation between IHC and NGS in 23 cases. In 8 (35%), there was diagnostic confirmation of IHC by NGS, and in 15 cases (65%) there was diagnostic exclusion of LS by IHC and NGS. In three cases, there was confirmation of a pathogenic variant in MLH1 by NGS. The cases presented the same large deletions, contradicting IHC with proficient MMR. A moderate correlation between IHC and NGS has been established, as indicated by the Kappa coefficient of 0.410 utilizing the Amsterdam II clinical criteria.