Abstract B082: Assessment of prevalence and utilization of tumor mutational burden and microsatellite instability in cancer patients at a community cancer center

Abstract Introduction: Molecular testing in the age of precision oncology can assist physicians in selecting individualized therapies. Biomarkers such as tumor mutational burden-high (TMB-H) and microsatellite instability-high (MSI-H) can predict response to immunotherapy. Since most cancer patients are treated in community cancer centers, the data on the utilization of these biomarkers in these settings are crucial. Methods: We conducted a retrospective study of 179 patients with advanced cancers who underwent genomic testing at our cancer center in 2021. We analyzed the prevalence of TMB-H (≥10 mutations/Mb) and MSI-H in this group, cancer type distribution, immunotherapy administration, and germline testing rates. Results: Out of 179 patients, TMB-H was found in 15.6% of cancers, and MSI-H was detected in 3.9% of cancers. Median age range was 71-80 years. Stage-IV disease was seen in 89% of the TMB-H and 100% of MSI-H patients. Non-small-cell-lung cancer was the most common tumor type among TMB-H, while unknown primary tumors were the most common among MSI-H patients. Only two patients (29%) with MSI-H underwent germline testing. Ten patients (36%) with TMB-H and two patients (29%) with MSI-H received immunotherapy. This translated into a combined immunotherapy uptake of 34%. Common reasons for underutilization of immunotherapy included patient deterioration and death before treatment initiation, or potential clinical judgment of the physician regarding the benefit of the treatment. Conclusion: These findings demonstrate that implementing TMB-H and MSI-H testing is not only feasible but also has a meaningful impact on treatment decisions. The results showed that the prevalence of these markers in the cohort was similar to the national datasets such as KEYNOTE-158 and TCGA. However, immunotherapy use was lower than that of larger academic centers. Furthermore, germline testing for Lynch syndrome screening remained underutilized. Interventions such as implementing early testing, provider education, and structured clinical pathways, including molecular tumor boards, can bridge these gaps. Citation Format: Safwan Muhammad, Mumta Essarani, Stephanie McClellan, Rishi Sawhney. Assessment of prevalence and utilization of tumor mutational burden and microsatellite instability in cancer patients at a community cancer center [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr B082.