249 Background: In patients with metastatic breast cancer, clinical practice guidelines include obtaining histologic confirmation of metastases when possible. The purpose of this study was to investigate patterns and correlates of receipt of a confirmatory biopsy. Methods: Data were abstracted from the records of patients diagnosed with metastatic breast cancer in the Michigan Breast Oncology Quality Initiative (MiBOQI), a statewide registry of 25 health systems. Patients with Stage IV disease at diagnosis were excluded. Analyses investigated associations between receipt of a confirmatory biopsy and disease, clinical and non-clinical factors, and treating health system. Results: Data were available for 1,231 (96%) of eligible patients between 2006 and 2015. Of these, 66% had a confirmatory biopsy; the proportion of patients having a biopsy varied between the 25 sites from 41% to 100% (p = 0.03). In bivariate analyses, younger age (p = 0.02), lower comorbidity (p = 0.007), longer time between the primary and recurrence (p < 0.001), more recent year of recurrence (p = 0.01), having liver, skin, soft tissue, or multiple metastases (p < 0.001), and private or government insurance (p = 0.002) were associated with biopsy. In multivariate analyses, longer time since the primary diagnosis (p < 0.001), more recent year of recurrence (p = 0.03), initial site(s) of recurrence (p < 0.001), and private or government insurance (p = 0.004) remained significant predictors of biopsy. Treatment site was no longer significant (p = 0.14). Minority status, obesity status, and disease characteristics (stage, estrogen receptor, progesterone receptor, HER2, grade) of the primary were not significant in either bivariate or multivariate analyses. Analyses were repeated without insurance with no change in the other findings. Conclusions: In a statewide collaborative, the proportion of patients having a confirmatory biopsy increased over the study period and was associated with several clinical factors. Insurance was an independent and significant predictor of receipt of what is considered standard care.
