Abstract PO5-04-07: Characteristics of patients with metastatic HR+/HER2+ breast cancer in a Kaiser Permanente observational multi-site cohort

Abstract Background: Approximately 10% of female breast cancer and 13% of male breast cancer tumors express hormone-receptor positive/human epidermal growth factor receptor 2 positive (HR+/HER2+) molecular subtype. Since HER2+ targeted agents were made available nearly 10 years ago, there has been limited innovation in treatment of patients with HR+/HER2+ metastatic breast cancer (mBC) to improve clinical outcomes. This study aims to characterize the HR+/HER2+ mBC patient population by describing demographic and clinical characteristics and treatment patterns in a racially diverse, insured, population-based cohort. This study includes data from 4 regions of the Kaiser Permanente (KP) health system – Northwest, Northern California, Southern California, and Colorado. Methods: Eligible study patients were adults age 18 years with HR+/HER2+ invasive breast cancer who were either initially diagnosed with Stage IV disease or were diagnosed at an earlier stage and experienced recurrence with distant metastasis between 6/8/2012 and 12/31/2019 with data collected through 12/31/2021. Select information was extracted from electronic health records (EHR) of eligible patients and combined with manually abstracted data to create the analytic dataset. Breast cancer recurrence was identified by tumor registrars or obtained through a breast cancer recurrence detection algorithm and verified by chart review. Chart reviewers collected data on metastatic sites, disease progression, reasons for stopping systemic therapy medications, and verified use of medications. Preliminary results: During the study period, we identified 492 subjects with HR+/HER2+ mBC. Seven were men and 485 were women. 221 (45%) had de novo Stage IV breast cancer at diagnosis and 271 (55%) had recurrent mBC. Median age at metastatic diagnosis was 59 years for de novo cases and 62 years for recurrent cases. The cohort was racially and ethnically diverse, with 13% Asian subjects (11% de novo, 15% recurrent), 12% Black subjects (10% de novo, 14% recurrent), and 66% White subjects (71% de novo, 63% recurrent). 18% of cases were recorded as Hispanic (19% de novo, 18% recurrent) in the EHR. Major sites of metastases, including bone, liver, lung, brain, and distant lymph nodes, were similar in both the de novo and recurrent groups. Among women (see table below), 28 (6%) received no systemic treatment for their metastatic disease (9% de novo, 3% recurrent). Among women with systemic treatment, 80% received anti-HER2 agents (90% de novo, 73% recurrent). Of women with recurrent mBC who received systemic therapy, 56% had received anti-HER2 therapy in the adjuvant setting. Conclusion: This population-based study of a racially diverse cohort examined EHR-derived data to describe current demographics and treatment patterns for HR+/HER2+ mBC in an insured patient population. Over 90% of women received systemic therapy, and the majority of those received anti-HER2 therapy per current treatment guidelines. Future analyses will focus on clinical outcomes in this cohort with a goal of informing how prognosis can be improved. Table. Citation Format: Sheila Weinmann, Debra Ritzwoller, Marilyn Kwan, Reina Haque, Stella Stergiopoulos, Ashley Cha, Eric Gauthier, Daniel Sapp, John Dickerson, Kathryn Richert-Boe, Weiming Hu, Nikki Carroll, Lie Hong Chen, Valerie Lee, Ravi Zalavadia, Maureen O'Keeffe-Rosetti. Characteristics of patients with metastatic HR+/HER2+ breast cancer in a Kaiser Permanente observational multi-site cohort abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-04-07.