Abstract PO-224: Socioeconomic and care setting gaps in guideline-recommended KIT mutation testing for gastrointestinal stromal tumor patients
Authors: Iorgulescu Bryan 
Published: December 2020

Abstract
Background: KIT gene mutations, involving approximately 80% of gastrointestinal stromal tumors (GISTs), are effectively targeted with tyrosine kinase inhibitor therapies (e.g. imatinib). As a result, NCCN guidelines strongly recommend testing all GISTs for KIT mutations. Herein we evaluate whether GIST patients face any barriers to KIT mutation testing. Methods: Patients ≥20-years-old newly-diagnosed with histopathologically-confirmed GISTs from 2010-2016 were identified from the National Cancer Database, which comprises &gt;70% of all newly-diagnosed cancer patients in the U.S. Patients were excluded if they lacked data about KIT mutation testing or were initially diagnosed at another institution. Patient demographic, socioeconomic, and care setting characteristics were evaluated for association with KIT testing using multivariable logistic regression. Results: 6,380 newly- diagnosed GIST patients were identified, only 62.8% (n=4,006) of whom received KIT mutation testing: increasing from 57.3% in 2010 to 70.9% in 2016. In multivariable analysis, patients who were ≥80-years-old (adjusted odds ratio [aOR] 0.81, 95% confidence interval [95%CI] 0.67-0.99, p=0.04), residing in ZIP codes of low high school graduation rates (referent &lt;6.3% no high school degree, 6.3-10.8% aOR 0.81, 95%CI: 0.69-0.95, p=0.01; ≥17.6% aOR 0.63, 95%CI: 0.50-0.78, p&lt;0.001), diagnosed at comprehensive community cancer hospitals (aOR 0.86 vs. academic/NCI-designated programs, 95%CI: 0.76-0.98, p=0.02) or hospitals in the western U.S. (aOR 0.81 vs. northeast, 95%CI: 0.67-0.97, p=0.02) were independently less likely to be tested. Notably, testing was independent of patients’ sex, race/ethnicity, insurance status, and median household income of their ZIP code.
Additionally, patients without KIT mutation testing were independently less likely to receive systemic therapy (i.e. tyrosine kinase inhibitors, aOR 0.69, 95%CI: 0.61-0.79, p&lt;0.001) even after adjusting for the aforementioned variables and GIST stage.
Conclusions: A majority of GIST patients now receive guideline- recommended KIT mutation testing. Fortunately, utilization of testing appears independent of patients’ race/ethnicity, insurance status, and household income status. However, some gaps in appropriate testing remain for elderly patients, for patients from counties of lower educational attainment, and for patients diagnosed at comprehensive community hospitals or hospitals in the western U.S. Importantly, underutilization of KIT mutation testing was independently associated with a reduced likelihood of receiving systemic therapy (i.e. tyrosine kinase inhibitors).
These findings highlight the need for additional research into the socioeconomic and care setting barriers to appropriate KIT mutation testing for GIST patients.
Citation Format: Bryan Iorgulescu. Socioeconomic and care setting gaps in guideline-recommended KIT mutation testing for gastrointestinal stromal tumor patients [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-224.