Clinicopathological Characteristics of Colorectal Carcinoma in Adults and Demonstration of Microsatellite Instability

Abstract

BACKGROUND Colorectal cancer (CRC) is one of the leading causes of mortality and morbidity from cancer. The risk group ranges from 69-79 years and the mean age being 62 years. Studies have shown that the percentage of patients under 50 years of age has increased to approximately 12 %. Colorectal carcinoma in young is usually located in the distal colon and is associated with aggressive behaviour, diagnosed at an advanced stage or maybe part of one of the hereditary colorectal syndrome. 12 - 15 % of carcinomas develop through microsatellite instability and 2 - 5 % are hereditary. Tumours with microsatellite instability are recognised by the absence of immunohistochemical staining for mismatch repair proteins (MLH1, MSH2, MSH6, PMS 1, and PMS 2) which is associated with Lynch syndrome. It is important to recognise tumours with MSI because of implications for genetic counselling, increased risk of secondary malignancy of colon or other organs, and in some settings, differences in prognosis and management. The study was intended to assess and compare the clinicopathological characteristics of colorectal carcinoma in adults above and below 50 years and also study the expression of MLH1 for demonstration of microsatellite instability in colorectal carcinoma. METHODS It was a retrospective study carried out in the Department of Radiodiagnosis, at Justice K. S. Hegde Charitable Hospital, from March 2020 to March 2021 after receiving ethical clearance from the institutional ethical committee. The study included a total of 90 patients. Patients were categorized into three different age groups, 18 - 25 years, 26 - 40 years and 41 - 55 years of age. RESULTS Clinicopathological features of 61 cases were studied and the mean age was 61 years. Most cases were left-sided cancer with moderately differentiated classical adenocarcinoma being the most common histopathological subtype. Individuals less than 50 years presented with adenocarcinoma with mucinous and signet ring cell morphology and with poor differentiation. 67.2 % had no lymphovascular invasion. The majority of the cases were positive for MLH1. The cases which showed negativity for MLH1 were cases with mucinous differentiation or signet ring cell type and were predominantly moderate to poorly differentiated and this relation was found to be significant. CONCLUSION The study concludes that the majority of CRC occurred in individuals between 61 - 70 years of age, they were left-sided moderately differentiated adenocarcinomas with stage IIB disease, most were negative for lymphovascular invasion and tumour infiltrating lymphocytes. Younger patients had a higher percentage of mucinous and signet-ring cell histology. 78.7 % were positive for MLH1. KEY WORDS Colorectal carcinoma, MLH1, Microsatellite instability