A study on the frequency and clinicopathological correlates of mismatch repair-deficient colorectal cancer

Introduction: Microsatellite instability is an important pathway of tumorigenesis in colorectal cancer, and there is a need to understand its genetic and phenotypic profile. This study aimed to study the occurrence of deficient mismatch repair (dMMR) in an Indian cohort of patients and document the corresponding clinicopathological correlates. Materials and Methods: This is a retrospective study of patients admitted between January 2016 and December 2017. dMMR data from immunohistochemistry reports were correlated with histopathological data and demographic details. The data were then analyzed in terms of means and percentages. Results: About 29% of cases were found to be dMMR and 66.7% of dMMR tumors occurred in males. About 44.4% of dMMR tumors occurred in the ascending colon. MSH2 loss was seen in 44.4% of cases while MLH1 loss was seen in 33.3%, and there were two cases with loss of PMS1. Conclusions: dMMR tumors in our study were more common in males, presented earlier, were bulky, were less likely to show lymphovascular or perineural invasion, had lower preoperative carcinoembryonic antigen levels, and yielded high number of lymph nodes. Expected differences in age, stage, and grade were not observed. Compared to other studies, a higher proportion of cases in our study had MSH2 and PMS2 loss.