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Study Finds Disparities in Microsatellite Instability/Mismatch Repair Biomarker Testing for Patients With Stage IV Colorectal Cancer


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Immune checkpoint inhibitors have improved outcomes for patients with a variety of cancer types, including those with advanced colorectal cancers that test positive for microsatellite instability/mismatch repair deficiency (MSI-high/MMRd). While testing rates for patients with MSI-high/MMRd advanced colorectal cancer have improved in recent years, a study by Lamba et al found such testing is underutilized in patients who are older, of Black non-Hispanic race/ethnicity, uninsured or Medicaid-insured, or diagnosed at community programs. The study was presented during the American Association for Cancer Research (AACR) Virtual Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved (Abstract PO-091).

Study Methodology

The researchers analyzed data from the National Cancer Database on 45,326 patients age 20 and older who newly presented with histopathologically confirmed stage IV colorectal adenocarcinoma from 2010 to 2016. Patients were excluded from analysis if they lacked data about MSI/MMR testing or were initially diagnosed at another institution.

Patients’ demographic, socioeconomic, and care setting characteristics were evaluated for association with MSI/MMR testing, as well as between MSI/MMR testing and the receipt of immunotherapy, using multivariable logistic regression.

“MSI/MMR testing rates for [patients with] stage IV colorectal cancer have dramatically improved in recent years, but appeared underutilized in patients that were older, of Black non-Hispanic race/ethnicity, uninsured or Medicaid-insured, or diagnosed at community programs. Our findings suggest that socioeconomic and care setting opportunities exist for improving access to testing of this important biomarker."
— Lamba et al

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Findings

The researchers found that of the 45,326 patients with newly diagnosed stage IV colorectal cancer, only 26.5% (n = 11,998) received MSI/MMR testing—rising from 14.4% in 2010 to 41.1% in 2016 (adjusted odds ratio [aOR] = 1.26/year, 95% confidence interval [CI] = 1.25–1.29, P < .001). Overall, patients who were older (referent 60–69 years old; 70–79 years old, aOR =  0.83, 95% CI = 0.77–0.89,  P < .001; 50–59 years old, aOR = 1.25, 95% CI = 1.16–1.33, P < .001), male (aOR = 0.94, 95% CI = 0.90–0.99, P = .01), or of Black non-Hispanic race/ethnicity (aOR = 0.87 vs White non-Hispanic, 95% CI = 0.82–0.94, P < .001) were independently less likely to receive testing.

Additionally, patients who were either uninsured (referent private insurance, aOR = 0.78, 95% CI = 0.70–0.86, P < .001), Medicaid-insured (aOR = 0.87, 95% CI = 0.80–0.94, P = .001), or Medicare-insured (aOR = 0.87, 95% CI = 0.81–0.93, P < .001); or diagnosed at community programs (referent academic/National Cancer Institute–comprehensive cancer program, aOR = 0.60, 95% CI = 0.56­–0.66, P < .001) or comprehensive community (aOR = 0.76, 95% CI = 0.72–0.80, P < .001) cancer programs were also significantly less likely to be tested. Even for those diagnosed in 2016, untested patients received independently less immunotherapy than tested patients (aOR = 0.61, 95% CI = 0.53–0.68, P < .001).

“MSI/MMR testing rates for [patients with] stage IV colorectal cancer have dramatically improved in recent years, but appeared underutilized in patients that were older, of Black non-Hispanic race/ethnicity, uninsured or Medicaid-insured, or diagnosed at community programs. Our findings suggest that socioeconomic and care setting opportunities exist for improving access to testing of this important biomarker,” concluded the study authors.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
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