Presentation (CTI)

OBJECTIVES: In 2017, cancer treatment guidelines recommended that all patients diagnosed with colon cancer undergo mismatch repair (MMR) genomic testing. Differences in genomic testing may worsen disparities in precision medicine use and survival. In this study, we describe disparities in MMR testing in patients with colon cancer.
METHODS: We used the Medicare 100% Research Identifiable Files (RIF) to identify patients with incident colon cancer diagnosed in 2022. We require a 1-year washout period prior to diagnosis. Our outcome was receipt of MMR testing 30 days before, or 90 days after, diagnosis. We measured the association between our outcome and age (65-74 years, 75-84 years, and 85+ years), sex, racial/ethnic group (American Indian/Alaska Native, Asian/Pacific Islander, Black, Hispanic, and White), Part D low-income subsidy, and zip code level median household income quartile.
RESULTS: We identified 20,806 patients with incident colon cancer; 11,772 (56.6%) used MMR testing. Patients who received the Part D low-income subsidy were less likely to use genomic testing relative to patients who did not receive the subsidy (48.6% vs 58.4%, p<0.001). Testing differed by median income quartile (p<0.001). Testing was lowest among the following patient subgroups relative to other patients in the corresponding category: male (55.6%), Hispanic (49.0%), and age 85+ years (50.6%).
CONCLUSIONS: This study highlights underutilization and disparities in MMR testing use among Medicare beneficiaries with colon cancer. Almost half of our cohort did not receive care recommended for all patients. The proportion of patients who underwent MMR testing increases with higher median income. Among patients who received MMR testing, the proportion of low-income subsidy non-recipients was 20.2% higher than low-income subsidy recipients. Future work may evaluate whether access to precision medicine and survival differ by genomic testing use and prompt stakeholders to increase access.