Clinicopathological and Histomorphological Evaluation of Colorectal Cancers for Features of Microsatellite Instability

Introduction: Colorectal Cancer (CRC) is the fourth most common cancer in men and third most common cancer in women. Microsatellite Instability-High (MSI-H) is a distinctive feature of Hereditary non-polyposis CRC syndrome (HNPCC) and it accounts for 15% of sporadic CRC. Identification of MSI-H colorectal tumours serves as a prognostic marker of patient outcome, as a predictive marker of response to chemotherapy and as a screening tool for HNPCC. Aim: The purpose of this study was to describe the clinical presentation and the histomorphological features of MSI. Materials and Methods: An ambispective type of validation study was carried out in Father Muller Medical College Hospital, Mangalore, Karnataka, India. The total duration of the study was 2.5 years. Whereas case collection was done from October 2017 to April 2019 for a period of 17 months. Surgical resection specimens of all the age groups for CRC were included in the study. Relevant patient history and clinical details were noted. Histomorphological features for MSI in CRC were noted using Revised Bethesda Guidelines. The results were analysed using Chi-square test. Results: A total of 104 cases were analysed during the study period. Majority of the patients with CRCs were in the age group of 51-60 years (30 cases, 28.84%), followed by 61-70 years age group (25 cases, 24.03%). Out of 104 cases, 72 (69.23%) of them were located in distal colon and among the various histomorphological types, adenocarcinoma accounted for 93 (89.42%) cases. Forty-nine (47.11%) of them were found to be in stage III disease. Crohn like lymphocytic reaction was a frequent histomorphological feature of MSI in about 50 (48.07%) cases of CRCs. Conclusion: The IHC test is the gold standard for MSI testing and most literature on Hospital-based study recommend IHC as the first line of testing. Identification of MSI-H by conventional histopathology by following Revised Bethesda Guidelines can be used as a screening tool for rapid selection of sporadic CRC for molecular testing, with the potential to recover a majority of MSI-H cases. MSI-H have better prognosis than stable cancers. MSI, particularly in stage II CRCs have better prognosis and do not benefit from 5FU- based adjuvant chemotherapy. Therefore, it is the most important prognostic marker in CRC and especially in stage II CRC.