Board's thesis at University of Basrah - College of Medicine discussed a pathological study of colorectal cancer and its relationship with the repair of genetic mismatch. The thesis presented by student Hala Abdulaziz Mahmoud aims to assess the occurrence of genetic mismatch repair in colorectal cancer and its relationship with pathological and clinical criteria (age, sex, histological tumor type, degree of histological differentiation, location and stage of the tumor). The thesis concluded that the application of histological immunohistochemical stains (MLH1,MSH2,PMS2,MSH6) have an important role in evaluating patients with colorectal cancer in order to detect microsatellite instability. The majority of cases with microsatellite instability were females with grade II tumor in stage II disease.