Abstract P6-01-27: Utilization of the Oncotype Dx Assay for Young Patients with Early Stage, Hormone-Receptor Positive, HER2-Negative Breast Cancer in an Integrated Health System

Abstract Background: Oncotype Dx (ODX) is one of the most widely used prognostic multigene expression assays for early-stage, hormone receptor-positive (HR+), HER2-negative (HER2-) breast cancer. Previous studies demonstrated reduction in chemotherapy in patients with a low ODX Recurrence Score (RS). Over recent years, utilization of this tool has increased in young breast cancer (YBC) patients (age≤40 years), a population often underrepresented in randomized clinical trials. The purpose of this retrospective study was to assess the utilization of this assay over time in an integrated health system and whether ODX RS results altered clinical practice. Methods: YBC patients with T1-T2N0 HR+HER2- breast cancer were retrospectively evaluated. Descriptive analysis examined the association between tumor characteristics, year of diagnosis, ODX testing, treatment, and recurrence outcomes. ODX risk categories were defined as: low risk 0-15; intermediate risk 16-25; high risk > 25. Recurrence was determined by the date of confirmation on pathology or imaging. Bivariate analysis compared characteristics between groups using Fisher exact tests for categorical variables and t-tests and nonparametric tests for continuous variables. Results: From 2008-2018, 1,436 Stage I-III YBC patients were diagnosed with invasive breast cancer, and 455 met eligibility criteria for ODX testing. Median follow-time (interquartile range, IQR) was 4.9 (2.8, 7.9) years for the 255 women who were tested and 5.7 (3.5, 8.7) years for the 200 women who were not tested (p< 0.05). Prior to 2018, 52.1% of patients were tested; after 2017, ODX testing rate increased to 88%. Overall, there were 255 patients who underwent ODX testing (55.9%). The median age (IQR) of patients who had an ODX test was 38.0 (35.0, 39.0). Of 225 tested patients, 42.0% (n=107) were White, 6.3% (n=16) Black, 33.7% (n=86) Asian/Pacific Islander, 15.7% (n=40) Hispanic, and 2.3% (n=6) identified as Other. There was no overall difference in testing based on ethnicity (p=0.42). More patients with grade 1 versus grade 3 disease were tested, 61.5% vs 45.2% (p=0.02 from overall Fisher exact test). Adjuvant chemotherapy was administered to 61.0% (122/200) patients who were not tested, whereas 38.4% (98/255) of those tested received chemotherapy (p< 0.001). In tested patients, 6% of low-risk (RS 0-15), 37% of intermediate risk (RS 16-25), and 92% of high risk (RS >25) patient received adjuvant chemotherapy. Among patients with T2 lesions, a higher proportion not tested (90.8% [59/65]) received adjuvant chemotherapy compared with those not tested (57.1% [40/70]). There were no differences in recurrence based on ODX testing, 11.0% (22/200) not tested vs. 9.4% (24/255) tested (p=0.26). Conclusions: Utilization of ODX testing increased after 2017. A significantly lower proportion of women who underwent ODX testing received chemotherapy, compared with women not tested for ODX. A higher percent of women with T2 cancer received chemotherapy if testing was not completed, which may reflect a greater fear of recurrence in younger patients. Further investigation is needed to better understand this potential risk of overtreatment in the YBC population. Citation Format: Ashley Aller, Jeanne A. Darbinian, Raymond Liu, Gillian Kuehner, Alison Savitz, Patience Odele, Laurel Habel, Brooke Vuong. Utilization of the Oncotype Dx Assay for Young Patients with Early Stage, Hormone-Receptor Positive, HER2-Negative Breast Cancer in an Integrated Health System [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-27.