Mismatch repair deficiency confers worse survival in stage IV colon cancer.

Background: Metastatic colon cancer (MCC) is a debilitating condition with a poor prognosis. Currently, there is limited data that investigates MCC in relation to mismatch repair (MMR) status. The aims of this study are to compare sociodemographic and clinicopathologic features and mortality between patients with MMR-proficient (MMR-P) and MMR-deficient (MMR-D) MCC. Methods: We performed an 8-year retrospective review of the National Cancer Database (NCDB) to identify patients age ≥18 years with MCC and reported MMR status. Data collection included sociodemographic characteristics, primary tumor sites and histopathologic features, and treatment modalities. Outcomes included 90-day, 180-day, 1-year, and 2-year overall mortality. Bivariate logistic regression and multivariate Cox regression identified differences between MMR-P and MMR-D and identified predictors of mortality, respectively. Results: A total of 10,922 MCC cases were identified; 8,796 (80.53%) were MMR-P and 2,126 (19.47%) were MMR-D. MMR-D was independently associated with older age at diagnosis, female sex, mucinous adenocarcinoma, medullary carcinoma, and lymph-vascular invasion. MMR-P was independently associated with perineural invasion and left-sided colonic primary tumor predominance. When adjusted for demographics, histology, and treatment modalities, MMR-D was associated with mortality at 180 days, 1 year, and 2 years. Conclusions: Our study identified several key sociodemographic and clinicopathologic features of MMR-D MCC. MMR-D appears to confer increased overall mortality at 180 days, 1 year, and 2 years after diagnosis in MCC.