LAUSR

224Background: Clinical practice guidelines in patients with metastatic breast cancer recommend assessment of biomarkers—estrogen receptors (ER), progesterone receptors (PR), and HER2—on metastatic lesions. The purpose of this study was to identify factors associated with assessment of these biomarkers in patients who had undergone confirmatory biopsies. We were particularly interested in variation between treatment sites. Methods: Eligible patients were those diagnosed with metastatic breast cancer who had undergone a confirmatory biopsy and who were part of the Michigan Breast Oncology Quality Initiative (MiBOQI) registry, a statewide registry of 25 health systems. Analyses investigated associations between assessment of ER, PR, HER2 and treating center, disease, clinical and non-clinical factors. Results: Between 2006 and 2015, 805 patients had a confirmatory biopsy. Of these, 66% had ER, 63% had PR, 62% had HER2, and 57% had all three assessed on the biopsy specimen. In bivariate analysis, characteris...