colorectal polyps occur at younger age and have a greater appetency for being malignant in patients with Lynch syndrome. However, some studies suggest that miss match repair(MMR) proteins mutation in colorectal polyps in patients younger than 50 play role in progression to colorectal cancer, but also other studies do not suggest miss match repair proteins mutation screening. Our goal was to specify the incidence of MMR proteins mutation in patients with adenomatous polyps under age 50 to find high risk group for lynch syndrome

We found patients between 18 to 50 years who removed colorectal polyps endoscopically from three referral pathology laboratory in Mashhad, Iran between 2014 and 2017. Familial history was taken with telephone interview. We performed IHC for four miss match repair proteins (MLH1, MSH6,MSH2 and PMS2) in adenomas

50 patients were identified with colorectal polyps. Out of 50 patients 27(54%) were male and mean age was 41. 24±6.5.None of our patients had family history of colorectal cancer but 7(14%)had lynch syndrome related cancers in their family. Of 50 examined polyps 26(52%) were tubular,20(40%)were tubulovillous and 3(6%) were serrated.84% of polyps were located in distal colon.34(68%) of adenomatous polyps were diagnosed with high grade dysplasia and 35(70%) were advance polyps (>1cm, high grade dysplasia, villous adenoma). Among 50 polyps which tested for MSI, none demonstrated MLH1, MSH2, MSH6 and PMS2 expression.

According to our findings IHC screening of adenomatous polyps in patients younger than 50 for MMR defect is not an effective tool for identifying HNPCC.