Do tumor localization, microsatellite instability and mismatch repair deficiency have an impact on the prognosis of colorectal cancer?

Background: Recent reports have shown that left-and right-sided colon cancers display different clinical and biological features. Chromosomal instability, epigenetic alterations, and defects in the deoxyribonucleic acid (DNA) mismatch repair (MMR) system may lead to the development of colorectal cancer (CRC). Besides microsatellite instability (MSI) caused by DNA MMR activity degradation increases the risk for CRC.

Aim: We aimed to show the differences between CRCs in different locations, to research the cause of these differences, to present whether there is a relation between MMR and MSI, and to evaluate their effects on prognosis.

Patients and methods: 641 CRC cases were divided into three groups: Group 1 (right-sided), Group 2 (left-sided), and Group 3 (rectum). Demographics, cancer stages, location of the tumors, number of the lymph nodes removed, MMR deficiency or proficiency, MSI status, and survival were assessed by retrospective review of the patients.

Results: Among 641 patients, 64.9% were males. Group 1, 2, and 3 comprised 31.2%, 45.7%, and 23.1% of all the cases, respectively. There was a significant difference in terms of survival and location only in stage II tumors. Stage II left colon cancer (LCCs) had a statistically significant lower survival rate. There was no significant difference in survival between both MSI and MMR statuses. In addition, cases were also stratified by stages. According to this data, 10.1, 45.7, and 44.2% of the patients had stages I, II, and III disease, respectively.

Conclusions: Although it was not statistically significant, tumors with MMR deficiency (dMMR) and high microsatellite instability (MSI-H) are more common in right-sided colon tumors.