Comparison of histopathologic and molecular features of microsatellite status in colorectal adenocarcinomas and its effect on survival

Colorectal cancers are among the most common malignant tumours worldwide and in our country. It basically develops through three different pathogenetic pathways. One of them, microsatellite instability (MSI), is caused by sporadic or hereditary mutations in DNA mismatch repair (MMR) genes. Approximately 15% of colorectal cancers develop through this pathway. Colorectal cancers with MSI have a better prognosis and treatment is different than those with microsatellite stable (MSS). In addition, the family should be guided in terms of Lynch syndrome, which is inherited. In this study, 224 cases diagnosed with colorectal adenocarcinoma between 2018 and 2022 in the Department of Pathology, Dicle University Faculty of Medicine were selected. H&E stained slides and MLH-1, PMS-2, MSH-2 and MSH6 immunohistochemical slides were retrieved from the archive and re-examined. General characteristics of the patients including histological subtype, gender and age, clinicopathological findings including pTNM, location, largest diameter of the tumour and presence of polyps, histomorphological findings including differentiation, molecular KRAS, NRAS and BRAF studies were obtained from Dicle University Faculty of Medicine Hospital Information and Management System and Medical Pathology archive records. Survival data were obtained from the Identity Sharing System accessed through the Hospital Information and Management System. Our aim was to compare these parameters with the MSI status of the cases. In our study, male gender, low metastasis rate, right colon location, large tumour diameter, low immature stroma and high tumour to stroma ratio were associated with MMR defective cases.No statistically significant correlation was observed between MSI status and tumour subtype, age, differentiation, pT stage, N stage, KRAS, NRAS and BRAF results, presence of polyps, presence of tumour nodules, intratumoural lymphocytic response level, presence of dirty necrosis and growth pattern. In our study, MMR genes were found to be defective in 26.3% of the cases. The rate of MMR defective CRC was higher compared to the literature. MMR stable v cases showed higher stroma ratio, immature stroma and more distant metastasis. However, in contrast to the literature and other findings, the survival of MMR stable patients was slightly better than MMR defective patients.