[Prevalence of altered mismatch repair protein nuclear expression detected by immunohistochemistry on adenomas with high-grade dysplasia and features associated with this risk in a population-based study].

Introduction: Alteration of mismatch repair system protein expression detected by immunohistochemistry (IHQ) in tumoural tissue is a useful technique for Lynch Syndrome (LS) screening. A recent review proposes LS screening through immunohistochemical study not only in all diagnosed cases of colorectal cancer (CRC) but also in advanced adenomas, especially in young patients.

Objective: To assess the prevalence of altered IHQ carried out in all adenomas with high-grade dysplasia (HGD) diagnosed in our community in 2011, as well as the variables associated with this alteration.

Methods: We included all the cases of adenomatous polyps with HGD diagnosed in the three public pathology laboratories of Navarre during 2011 and performed a statistical study to assess the association between different patient and lesion characteristics and altered IHQ results.

Results: A total of 213 colonic adenomas with HGD were diagnosed, and 26 (12.2%) cases were excluded from the final analysis (2 known LS, 22 without IHQ study and 2 with inconclusive IHQ studies). The final number of adenomas included was 187. Pathologic results were found in 10 cases (5.35%)-6 cases in MLH1 and PMS2, 2 cases in PMS2, 1 case in MSH6 and 1 case in MSH2 and MSH6. The factors showing a statistically significant association with the presence of abnormal proteins were the synchronous presence of CRC, the presence of only one advanced adenoma, proximal location of HGD and age <50 years.

Conclusions: The percentage of pathologic nuclear expression found in IHQ is high. Consequently, screening of all diagnosed HGD could be indicated, especially in young patients, with a single AA and proximal HGD.