The first comprehensive study to evaluate the prevalence and characteristics of LS CRC in the early-onset Iranian CRCs using a universal strategy.
Conducted using participants from one province in northeastern Iran.
Unable to contact all CRCs,; therefore, all consecutive CRCs were included.
Lack of germline mutation testing in clinical practice made differentiation between true lynch and lynch-like early-onset patients to be difficult.

Abstract
Purpose: Lynch Syndrome (LS), a genetically inherited autosomal disorder, increases the incidence of colorectal carcinoma (CRC). We aimed to assess the prevalence and clinicopathological characteristics of early-onset LS CRCs vs. late-onset ones in the Iranian population.

Methods: Retrospectively, 323 patients with CRC were screened between 2013 and 2016 in Mashhad, Iran. Information regarding the clinical criteria was obtained by interviewing the patients or, their families. Amsterdam II criteria, revised Bethesda guideline, and universal strategy waswere performed to screen CRCs. Pathologists tested Tumors 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.