Abstract 5550: Sociodemographic disparities in access to biomarker testing in patients with advanced colorectal cancer
Authors: Sabbagh Saad , Jabbal Iktej , Dominguez Barbara , Itani Mira , Mohanna Mohamed , Nagarajan Arun 
Published: June 2023

Introduction All patients with newly diagnosed colorectal cancer are recommended to undergo microsatellite instability (MSI) testing. In addition, mutational testing using biomarkers such as KRAS, NRAS, and BRAF is recommended for patients with metastatic cancers. Testing for these markers is vital as they guide therapeutic decision-making and serve as prognostic indicators. Our study aims to analyze disparities in testing for MSI and KRAS biomarkers based on sociodemographic factors in patients with metastatic colorectal cancer. Furthermore, we explored the survival characteristics in these patients based on sociodemographic factors and on access to biomarker testing.

Methods The National Cancer Database (NCDB) was queried for patients diagnosed with metastatic colorectal cancer (MCC). At the bivariate level, we performed chi-squared statistics and multivariate logistic regression modeling to explore variables associated with patients undergoing MSI and KRAS testing. In addition, Multivariate Cox regression and Kaplan-Meier analyses were performed for survival analysis.

Results N = 51,913 patients with MCC diagnosed between 2010 to 2017 were included. The median age for Whites was 68.0 years versus 64.0 years for Blacks. Blacks had a lower probability of undergoing MSI testing (OR 0.90, [0.84-0.96] p&lt; 0.0009). Factors associated with a lower likelihood for MSI testing included treatment at a Community Cancer Program (OR 0.61, [0.55-0.66] p&lt;0.0001), residing in areas with people having lower education (OR 0.68, [0.62-0.74] p&lt;0.0001) and in rural areas (OR 0.74, [0.61-0.90] p-value 0024), and a median household income of &lt; $38,000 (OR 0.88, [0.80-0.96] p 0.0040). Patients with no insurance and Medicaid/governmental insurance were also less likely to undergo both MSI and KRAS testing. Blacks had a decreased likelihood of having high MSI levels among patients who underwent testing compared to Whites (OR 0.67, [0.50-0.91] p-value 0.0107). After controlling for confounding variables, survival analysis showed poor survival in patients who did not undergo testing for MSI and KRAS (HR 1.20, [1.17-1.23] p&lt;0.0001 and HR 1.04, [1.01-1.06] p-value 0.0016 respectively).

Conclusion Our analysis reveals that sociodemographic factors such as being from a minority race, having no insurance, residing in areas with lower education and rural settings were associated with a lower probability of undergoing MSI testing in patients with metastatic colorectal cancer. This is of concern as our study also reveals that not undergoing biomarker testing is associated with poorer survival. Addressing such sociodemographic discrepancies among racial groups is essential in achieving equitable care and narrowing gaps in outcomes.

Citation Format: Saad Sabbagh, Iktej Jabbal, Barbara Dominguez, Mira Itani, Mohamed Mohanna, Arun Nagarajan. Sociodemographic disparities in access to biomarker testing in patients with advanced colorectal cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5550.