Mismatch repair deficiency testing in colorectal cancer and factors associated with nonadherence to guidelines.

Abstract

e16069 Background: Mismatch repair (MMR) deficiency is characteristic of Lynch syndrome, which typically affects patients < 50 years old with colorectal cancer (CRC) but can also occur in sporadic CRC. MMR deficiency causes microsatellite instability (MSI) and affects therapy response and prognosis. Guidelines now recommend universal testing of MMR/MSI in all CRC patients, but universal testing has not been achieved. Our study sought to evaluate factors associated with MMR/MSI testing in CRC patients. Methods: The National Cancer Database (NCDB) identified 433,968 patients diagnosed with stages I-IV CRC from 2011-2016. Variables included gender, race, stage, insurance status, education, income, and treatment facility type. Baseline characteristics were compared using Pearson's chi‐square test between patients not tested versus tested for MMR/MSI status. Multivariate logistic regression analysis determined the factors associated with increased probability of MMR/MSI testing. Results: Only 34.7% patients were tested for MMR/MSI and those £ 40 years old were more likely to be tested as were Caucasian patients. Patients with private insurance were more likely to be tested compared to uninsured (OR 1.21; 95% CI 1.1601.27, p < 0.001). Testing also correlated with increasing education, reported as the percentage of adults over 25 years old who did not graduate high school within a zip code. Diagnosis at an academic/research program was also a positive predictor of MMR/MSI testing compared to a community program (OR 1.74; 95% 1.71-1.77, p < 0.001). Testing was dependent on stage with the greatest likelihood of testing in stage II (OR 1.44, 95% CI 1.41-1.46, p < 0.001) and the least in stage IV (OR 0.72; 95% CI 0.71-0.74, p < 0.001) compared to stage I. Still, the trend for testing increased over the years (trend p < 0.001), with that in 2016 being 4 times more likely than in 2011 (OR 4.66; 95% CI 1.53-4.80, p < 0.001). Conclusions: Our study identified established risk factors affecting care such as African American race, treatment at a non-academic facility and being uninsured. It also showed age and stage were factors associated with noncompliance to new guidelines regarding testing for MMR/MSI with testing being less frequent in older patients and those with later stages. An explanation and study limitation is that NCDB only collected diagnoses until 2016 while immunotherapy in MSI-H or dMMR CRC was approved in 2017. With more treatment options available now to these patients, testing rates will hopefully improve with more research needed to capture this.