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Real-world practice patterns in the diagnosis of recurrent metastatic breast cancer in Washington state.

e13640 Background: Evidence-based, national guidelines for the diagnosis of recurrent metastatic breast cancer (MBC) recommend confirmation of recurrence with biopsy and reassessment of biomarker status. Real world practice patterns may demonstrate disparities in adherence to guidelines with implications for patients and health systems. Methods: We utilized the Hutchinson Institute for Cancer Outcomes Research (HICOR) data repository that links Washington State cancer registry data to enrollment and claims from the major insurance payers in the state. We identified women > 18 years old diagnosed with recurrent MBC between 2008 and 2017 with evidence of enrollment in a commercial plan (Premera or Regence), Medicare, or Medicaid. Recurrence in Stage I-III patients was detected through identification of ICD 9/10 codes for metastatic disease or resumption of breast cancer systemic therapy (after minimum of 4 months from completion of early breast cancer therapy). Using claims, we identified receipt of and factors associated with biopsy, biomarker re-assessment, and treatment administered at recurrence. Results: We identified 715 patients with recurrent MBC (any ER or HER2 status) with median age of 62 (range 52-73). The majority of the cohort were Caucasian (89%) 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 (97%). Approximately 13% of patients lived in areas of high deprivation (area of deprivation index, ADI, 8-10). Patients had either Commercial (53.1%), Medicaid (4.2%), Medicare (29.7%) or multiple (13.0%) insurance. Patients were primarily treated at high volume centers (70.9%), though 23% of patients were seen at low volume centers (<25 breast cancer patients/year). Of the patients with recurrent MBC, 49.5% received a biopsy to confirm metastatic diagnosis. Similarly, 48.7% of recurrent MBC patients underwent biomarker reassessment. Patients with highest co-morbidity index (>2) were more likely to undergo biopsy confirmation (20.3% vs 13.0%, p = 0.02). Biopsy was more often performed in patients receiving care at a high-volume center compared to low-volume center (74.3% vs 18.6%, p = 0.03). First line treatment selection was directly associated with receipt of biopsy and biomarker testing. Hormone therapy only was more common in patients who did not undergo biopsy (62.3% vs 37.7%, p <0.001) or biomarker reassessment (62.7% vs 37.3%, p <0.001). Conclusions: Our study shows there is variation across Washington state in biopsy and biomarker assessment in the diagnosis of recurrent metastatic breast cancer. Nearly half of cases had metastatic biopsy omitted. Our findings demonstrate downstream implications for treatment selection and support the need for quality initiatives to improve adherence to guidelines.