Abstract 3822: Oncotype DX testing and differences in use of chemotherapy by age in an integrated system

Abstract Introduction: Oncotype DX (ODX) identifies breast cancer patients who are less likely to benefit from chemotherapy. We investigated patient factors associated with clinical application of ODX testing and chemotherapy use. Methods: We identified a cohort of adult breast cancer patients with stage I-IIA, estrogen receptor positive, human epidermal growth factor receptor 2 negative, lymph node negative disease diagnosed within Kaiser Permanente Northern California between 2015 - 2021 eligible for ODX testing. Chi-square tests were used for bivariate analysis of categorical variables. Multivariable logistic regression was used to identify independent predictors of chemotherapy use in female patients with high risk ODX scores (>25). Results: 8017 patients were eligible for ODX testing; of which 5,136 received testing (64%) and 576 patients (7%) had high risk ODX. ODX testing increased over the years (45% of eligible patients in 2015; 79% of eligible patients in 2021). Testing was frequent in larger lesions (74%), poorly differentiated tumors (73%), and younger patients (83% in patients <40 years at diagnosis; 12% in patients > 80 years). Chemotherapy was frequently administered in younger patient, and for larger, poorly differentiated tumors. For patients who possessed a high risk ODX score, chemotherapy administration differed by age. In comparison with the 90% of high risk patients <45 years who received chemotherapy, 58% of patients 60+ years at diagnosis with high risk ODX received chemotherapy. Comorbidity index and chemotherapy administration was not statistically significant (Table 1). Conclusion: Oncologists frequently use ODX testing to guide chemotherapy management. Despite high risk ODX scores, older patients received less chemotherapy compared to their younger counterparts. Further investigation is needed to determine how age impacts clinician decision making and clinical outcomes following ODX testing. Table 1. Multivariable Logistic Regression Analysis of Factors Associated with Chemotherapy Women > 60 years with high risk oncotype DX scores (N=467) Adjusted Odds Ratio (95% Confidence Interval) P-values (Calculated using the Wald χ2 Statistic) Age at Cancer Diagnosis (Reference: 60 - 69 years old) 70-79 0.62 (0.40-0.96) 0.03 >79 0.11 (0.02-0.55) 0.01 Charlson Comorbidity Index (Reference = 0) 1 0.76 (0.48-1.22) 0.26 2 0.62 (0.30-1.29) 0.20 3 0.65 (0.26-1.60) 0.35 4 0.54 (0.20-1.44) 0.22 5+ 0.37 (0.10-1.35) 0.13 Citation Format: Ashley Aller, Liisa Lyon, Laurel Habel, Aida Shirazi, Raymond Liu. Oncotype DX testing and differences in use of chemotherapy by age in an integrated system [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3822.