Abstract 804: Temporal trends and disparities by race and ethnicity in treatment of women diagnosed with advanced hormone receptor-positive breast cancer: A SEER-Medicare analysis

Abstract Background: The clinical guidelines for management of advanced hormone receptor-positive (HR+) breast cancer (BC) have changed in the past decade with the addition of novel drug classes. We assessed temporal patterns of treatment initiation among women diagnosed with advanced HR+ BC and examined disparities in treatment initiation by race and ethnicity. Methods: Women aged ≥65 years diagnosed with stage IV or metastatic HR+ BC between 2010-2019 were identified in SEER-Medicare. Poisson models were used to estimate age-adjusted annual incidence rates (IR) and 95% confidence intervals (CIs) for treatment initiation within 12 months of BC diagnosis independently by human epidermal growth factor receptor 2 (HER2) status. Age-adjusted incidence rate ratios (IRR) and 95% CIs were estimated to compare rates of initiation among non-Hispanic Black (NHB) and Hispanic patients with non-Hispanic White (NHW) patients. Results: Among 3, 476 eligible patients with a mean age of 76. 7 (SD: 7. 5) years at diagnosis, 79. 6% were NHW, 9. 5% were NHB, and 6. 0% were Hispanic. Among 2, 668 women with HR+/HER2- BC, most initiated on aromatase inhibitors (AIs) alone (56. 7%), followed by AIs with palbociclib (12. 6%). There was a temporal increase in rates of initiation of AIs with palbociclib (IR 95% CI per 1000 person-years: 252. 8 240. 8, 265. 4 in 2015 and 343. 9 330. 8, 357. 7 in 2019. We did not observe significant differences in rates of initiation of AIs alone or with palbociclib by race and ethnicity. Among 537 HR+/HER2+ patients, 25. 0% initiated on AIs alone, 24. 6% on pertuzumab and trastuzumab with chemotherapy, 14. 3% on trastuzumab with chemotherapy, and 9. 1% on AIs and trastuzumab with chemotherapy. IRs (95% CI) for initiation of pertuzumab and trastuzumab with chemotherapy increased from 175. 6 (146. 3, 210. 9) in 2013 to 756. 5 (698. 3, 819. 5) in 2019, while rates for trastuzumab with chemotherapy declined from 963. 1 (809. 4, 1146. 0) in 2010 to 88. 4 (72. 6, 107. 5) in 2019. Rates of initiation of AIs and trastuzumab with chemotherapy remained constant over time. Compared to NHW, NHB and Hispanic women were less likely to initiate pertuzumab and trastuzumab with chemotherapy (IRR 95% CI: 0. 52 0. 27, 1. 00 and 0. 54 0. 24, 1. 23 respectively) and more likely to initiate AIs alone (IRR 95% CI: 2. 23 1. 39, 3. 55 and 2. 98 1. 69, 5. 24 respectively). Conclusions: We observed a temporal increase in the initiation of AIs with palbociclib among patients with advanced HR+/HER2- BC. Among patients with HR+/HER2+ BC, rates of initiating pertuzumab and trastuzumab with chemotherapy increased while rates of trastuzumab with chemotherapy declined. The observed differential management of NHB and Hispanic compared with NHW patients with HR+/HER2+ BC using pertuzumab and trastuzumab with chemotherapy and AIs alone requires further investigation. Citation Format: Kexin Zhu, Elisa Bandera, Farzin Khosrow-Khavar. Temporal trends and disparities by race and ethnicity in treatment of women diagnosed with advanced hormone receptor-positive breast cancer: A SEER-Medicare analysis 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 (6Suppl): Abstract nr 804.