Real-world practice patterns in treatment of metastatic breast cancer in Washington State.

e13038 Background: Evidence-based, national guidelines for the management of metastatic breast cancer (MBC) recommend numerous treatment options that do not capture the nuances of real-world practice. Disparities may exist across Washington State with financial implications for patients and health systems. The objective of this study was to assess practice patterns around treatment of ER+/HER2- MBC in actual clinical practice. Methods: We collaborated with Hutchinson Institute for Cancer Outcomes Research (HICOR) to link enrollment and insurance claims records with Washington State cancer registries from 2008-2017. Our cohort comprised of women >18 years old with de novo ER+/HER2- MBC who met enrollment criteria in one of four payors (Premera, Regence, Medicare, or Medicaid). We identified receipt of first line treatment, categorized as CDK4/6 inhibitors plus endocrine therapy (CDKi+ET), chemotherapy (CT), or endocrine therapy alone (ET). We examined factors influencing treatment selection using Fisher's and Kruskal-Wallis tests. Total costs (defined as costs from inpatient and outpatient claims one year after diagnosis) was estimated for patients and payors. Results: We identified 140 patients with de novo ER+/HER2- MBC with median age of 64 (range 28-95). The majority of the cohort were Caucasian (90%) with the rest comprising of Asian, Black, American Indian, and Hispanic patients. Based on the Rural Urban Commuting Area (RUCA) classification, patients predominantly lived in metropolitan neighborhoods (96%). Over 20% of patients lived in areas of high deprivation (area of deprivation index, ADI, 8-10). Patients had either Commercial (40.7%), Medicaid/Medicare (43.6%) or multiple (15.7%) insurance. Our data show that 17 patients (12%) received first line therapy with CDKi + ET, 64 patients (46%) with CT, and 59 patients (42%) with ET alone. Factors influencing treatment selection include age, co-morbidity score, and payor type. Older patients (>65 years old) were more likely to receive ET alone compared to younger patients (56% vs 44%, p value <0.001). Patients with high co-morbidity score were more likely to receive ET (30%) compared to CT (5%) or CDKi + ET (23%), p value <0.001. Patients with commercial insurance made up over 50% of patients in our cohort who received CDKi +ET, while Medicare-insured patients were most likely to receive ET alone (p value <0.001). We estimated the mean cost of receiving first line therapy with CDKi +ET ($20,368 and $175,932), CT ($10,624 and $117,847) and ET alone ($13,292 and $60,338) for patients and payors, respectively (costs inflated to December 2019). Conclusions: Our study shows substantial variation across Washington state in treatment selection and costs for patients with metastatic breast cancer in the first-line setting. Our findings demonstrate the need for initiatives to standardize quality of care relative to clinical guidelines in metastatic breast cancer care.