Lynch Syndrome in Colorectal Cancer Surgery

Study Design (Material and Methods) This is a multicentre, prospective cohort and audit study conducted in Türkiye. The study aims to evaluate the incidence of Lynch syndrome among patients who undergo surgery for colorectal cancer in participating general surgery departments. Over a 12-month period, patients undergoing surgery for histologically confirmed colorectal cancer at multiple tertiary hospitals across Türkiye will be enrolled. Postoperative pathological assessments will include immunohistochemical (IHC) analysis for mismatch repair (MMR) protein expression (MLH1, PMS2, MSH2, and MSH6). In cases showing loss of MLH1 and PMS2 expression, BRAF mutation testing will be performed. If BRAF mutation is detected, MLH1 promoter methylation analysis will follow. A positive result in both tests will suggest a sporadic etiology, whereas the absence of both findings will lead to referral for germline genetic testing using next-generation sequencing (NGS) to investigate Lynch syndrome. For patients with isolated MSH2 and/or MSH6 loss, direct referral to genetic testing will be carried out without BRAF or methylation testing. Patients with intact MMR expression will be recorded as the MMR-proficient control group. Comparative analysis will be conducted between dMMR and MMR-proficient patients, including demographic characteristics (age, sex, family history of cancer), tumor staging, anatomical location, and presence of metastases. The primary outcome is to determine the incidence of Lynch syndrome among surgically treated colorectal cancer patients in Türkiye and to identify clinical and pathological correlations.