The Prevalence and Prognosis of Microsatellite Instability-High/Mismatch Repair-Deficient Colorectal Adenocarcinomas in the United States

PURPOSE Microsatellite instability (MSI) and DNA mismatch repair (MMR) status is an indispensable biomarker in the management of colorectal cancers. We therefore examined the epidemiology of MSI-high/MMR-deficient colorectal cancers in the United States. METHODS Adults presenting with colorectal adenocarcinoma in 2018-2019 were identified from the US National Cancer Database. Attributes associated with MSI-high/MMR-deficiency were identified using multivariable logistic regression and reported using average adjusted probabilities (% AAP ) and 99.9% CIs. As a secondary aim, the survival associated with MSI/MMR status was assessed. RESULTS Among 101,259 colorectal adenocarcinomas in 2018-2019, 82.0% were microsatellite stable/MMR-proficient, 3.8% MSI-low, and 14.2% MSI-high/MMR-deficient—including 16.6%, 19.9%, 12.4%, and 7.3% of stage I, II, III, and IV cancers, respectively. In locoregional cancers, MSI-high/MMR-deficiency was associated with a bimodal age distribution, female sex, right-sided colonic origin, wild-type KRAS, and a prior diagnosis of cancer (all P < .001). By race/ethnicity, colorectal adenocarcinomas were MSI-high/MMR-deficient in 16.9% AAP of non-Hispanic White (99.9% CI, 16.5 to 17.4) patients, compared with 11.3% AAP of non-Hispanic Black (99.9% CI, 10.3 to 12.4), 12.4% AAP of Asian/Pacific Islander (99.9% CI, 10.5 to 14.3), and 15.1% AAP of Hispanic (99.9% CI, 13.4 to 16.7) patients (all P < .001). Histologically, MSI-high/MMR-deficiency was associated with increasing grade, from 11.3% AAP of well-differentiated tumors (99.9% CI, 10.2 to 12.4) to 28.4% AAP of poorly differentiated cases (99.9% CI, 27.1 to 29.8; P < .001). Compared with conventional histology (15.2% AAP , 99.9% CI, 14.8 to 15.6), medullary (41.1% AAP , 99.9% CI, 33.0 to 49.3; P < .001) and mucinous (24.6% AAP , 99.9% CI, 22.8 to 26.3; P < .001) subtypes—but not signet-ring cell histology (15.5% AAP , 99.9% CI, 11.6 to 19.4; P = .79)—were more frequently MSI-high/MMR-deficient when adjusting for clinicopathologic features including grade. CONCLUSION Our findings establish the epidemiology, features, and prognostic implications of MSI-high/MMR-deficiency among colorectal adenocarcinoma patients in the United States.