EP126 - Preparing for the New Commission on Cancer Microsatellite Instability Quality Measure in Colorectal Cancer: Opportunities for Improvement

Purpose/Background: Recent advances in immunotherapy have opened new avenues of treatment for colorectal cancers (CRC) with microsatellite instability (MSI), and therefore most treatment guidelines have incorporated testing at the time of diagnosis in their recommendations. A new quality measure has been developed by the Commission on Cancer (CoC) and the National Accreditation Program for Rectal Cancer (NAPRC) to measure compliance with MSI testing at the time of CRC diagnosis. In preparation for the new measure, we designed a study to identify factors associated with failure to perform MSI testing in CRC patients.

Methods/Interventions: This was a retrospective, single-institution study of colorectal cancer patients diagnosed and/or treated at our institution between 2018 and 2023. Patient demographic data, including age, sex, race, insurance status, zip code-based median household income (based on 2023 US Census data), and clinical data such as stage, pathology, and treatment were collected. Missing data were excluded from the analysis. Univariate analysis of categorical variables was performed using Pearson's Chi-squared test or Fisher's exact test for low expected counts. Univariate analysis of continuous variables was performed using t-test or Wilcoxon rank sum test for non-parametric distributions. Multivariable analysis was performed with multivariable logistic regression adjusted for age, sex, race, insurance type, zip code-based income, tumor site, stage at diagnosis, diagnosis year, diagnosing facility, initial treatment course, and surgical facility. Patients with a stage at diagnosis of "Other/Unknown" (n=20) and race of "Other" (n=6) were excluded from multivariable models due to small numbers.

Results/Outcomes: A total of 1,349 patients were included, of which 52 (3.85%) did not have documentation of MSI testing at diagnosis. On univariate analysis, older age, rectal cancers, early stage at diagnosis, and initial treatment other than surgery were associated with increased risk of MSI testing failure. Factors associated with decreased risk of MSI testing failure were diagnosis at outside facilities and surgery at our facility (Table 1). On multivariable analysis, failure to test for MSI was associated with rectal tumors (OR 2.23, 95% CI 1.11 - 4.55, p = 0.03). Decreased rates of MSI testing failure were associated with more recent year of diagnosis (OR 0.82, 95% CI 0.68 - 0.99 p = 0.04) and stage 2/3 (OR 0.27, 95% CI 0.13 - 0.56, p < 0.001) or stage 4 disease (OR 0.09, 95% CI 0.03 - 0.25, p < 0.001) (Table 2). The interaction between tumor site and stage at diagnosis was evaluated and found not to be statistically significant (likelihood ratio test p = 0.37).

Conclusion/Discussion: In our study, the lack of MSI testing in colorectal cancer patients has largely become rare but is more commonly associated with rectal cancers and patients with early-stage disease. Interestingly, rectal cancer was associated with a higher rate of failure, an area of the greatest promise for neoadjuvant use of immune checkpoint inhibitors. Overall, it is encouraging that there is a trend towards improved MSI testing over time; however, attention needs to be paid to this patient population to ensure they are receiving a complete work-up, including MSI testing at diagnosis. The new Commission on Cancer quality improvement measure will be a valuable tool to benchmark performance and improve compliance.

Table 1
Table 1 - Univariate comparison of patient demographics, tumor characteristics, and treatment variables by MSI testing status. Continuous variables are presented as mean ± SD or median [IQR]; categorical variables are presented as n (%). Abbreviations: MSI = Microsatellite Instability; SD = Standard Deviation; IQR = Interquartile Range.
Table 2
Table 2 - Multivariable logistic regression for factors associated with MSI testing. Adjusted for age, sex, race, insurance type, zip code-based income, tumor site, stage at diagnosis, diagnosis year, diagnosing facility, initial treatment course, and surgical facility. Values are odds ratios (OR) with 95% confidence intervals (CI). Abbreviations: MSI = Microsatellite Instability; Ref = reference.