Underutilization of Guideline-Recommended Mismatch Repair/Microsatellite Instability Biomarker Testing in Advanced Colorectal Cancer

Young-onset colorectal cancer

In the past decades the incidence of colorectal cancer (CRC) in people under the age of 50 years has increased, which is referred to as early-onset CRC or young-onset CRC (YO-CRC). YO-CRC is expected to account for 11% of colon cancers and 23% of rectal cancers by 2030. This trend is observed in different parts of the world and in both men and women. In 20% of patients with YO-CRC, a hereditary cancer syndrome is found as the underlying cause; however, in the majority of patients no genetic predisposition is present. Beginning in the 1950s, major changes in lifestyle such as antibiotic use, low physical activity and obesity have affected the gut microbiome and may be an important factor in YO-CRC development. Owing to a lack of screening, patients with YO-CRC are often diagnosed with advanced-stage disease. Long-term treatment-related complications should be taken into account in these younger patients, making the more traditional sequential approaches of drug therapy not always the most appropriate option. To better understand the underlying mechanism and define relationships between environmental factors and YO-CRC development, long-term prospective studies are needed with lifestyle data collected from childhood.

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.