Abstract
Abstract only
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Background: High-frequency microsatellite instability (MSI-H) accounts for roughly 15% of all cases of colorectal cancer (CRC). Studies suggest a significant non-adherence to routine MSI testing in patients diagnosed with CRC despite universal guidelines. Methods: We used the NCDB to identify adults with MSI-H status CRC from 2010-2015 with the following histologic subtypes: mucinous and not otherwise specified adenocarcinoma, and medullary carcinoma. The primary site was localized to the right colon, left colon, and rectum; demographic factors, clinicopathologic features, and treatments were identified. Patients were stratified by site and discrete and continuous variable comparisons were made using the chi-square and Mann-Whitney test, respectively. Survival was examined with the Kaplan-Meier method and a Cox proportional hazards regression model. A logistic regression model was used to examine MSI status. All analyses were conducted with SAS version 9.4. Results: A total of 5364 patients were identified and stratified by site into 3 groups: right colon (n = 4004, 74.6%), left colon (n = 890, 16.59%) and rectum (n = 470, 8.76%). Compared to the left colon and rectum, right colon patients were more likely to be older females with larger tumors and less likely to receive chemoradiation. After adjusting for all else, we found statistical evidence that female vs. male gender (OR = 1.47; 95% CI: 1.24 to 1.73), Black vs. White race (OR = 0.61; 0.45 to 0.83), left vs. right colon (OR = 0.33, 0.27 to 0.41), rectum vs. right colon (OR = 0.08, 0.05 to 0.13), mucinous adenocarcinoma vs. adenocarcinoma (OR = 2.37, 1.92 to 2.93), medullary carcinoma vs. adenocarcinoma (OR = 8.86, 4.56 to 17.22), positive vs. negative k-RAS mutation (OR = 0.49, 0.41 to 0.59), and positive vs. negative CEA status (OR = 0.79, 0.66 to 0.94) were factors associated with MSI-H status. Improved survival was associated were Hispanic white race, stage 1, and free surgical margins within a multivariable context. Factors associated with poor survival: increased Charlson/Deyo score, advanced stage, lymphovascular invasion, and positive CEA status. Conclusions: In settings where resources are scarce and universal testing is not possible, there is a benefit from MSI testing in female patients, those with right-sided colon cancer, mucinous adenocarcinoma, and medullary carcinoma.