Disparities in Biopsy Practice in Metastatic Breast Cancer Patients Managed in Community Oncology Practices in the United States

OBJECTIVES: The National Comprehensive Cancer Network guidelines recommend tumor phenotyping for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 at initial breast cancer diagnosis, with repeat biopsy considered at disease progression. This study assessed the frequency, timing, regional variation, and predictors of repeat biopsies among patients with metastatic breast cancer (mBC) treated at community oncology practices in the United States. METHODS: A weighted random sample of 911 mBC patients was selected from 15 practices within the ONCare Alliance network. The data included demographics, clinical characteristics, number and types of biopsies, and associated findings. Multivariate negative binomial regression, adjusted for disease duration, was used to identify predictors of biopsy frequency. RESULTS: Among the cohort, 42.2% had a history of early-stage disease, while 57.8% were diagnosed with de novo stage IV mBC. After adjusting for disease duration, patients with prior early-stage disease underwent significantly more biopsies (mean: 3.9; 95% CI: 3.7-4.0) than those with de novo mBC (mean: 2.2; 95% CI: 2.1-2.3; P <0.001). Factors associated with fewer biopsies included non-Black, non-Asian minority status (RR=0.80, P <0.001), longer time to metastatic progression (RR=0.93, P <0.001), poor performance status, and geographic region. CONCLUSIONS: A substantial proportion of patients with mBC, particularly those with de novo disease, did not undergo repeat biopsy at progression. These findings reveal disparities in biopsy practices and underscore the need for improved adherence to guideline-based care in community oncology settings.