Researchers hope to identify prognostic groups within a de novo metastatic cohort using both anatomic and biologic variables. However, the recommendations for stage IV illness do not account for how these characteristics may influence outcomes, anatomic and biologic considerations were now included in breast cancer staging. Investigators used the National Cancer Database (2010–2013) to find de novo metastatic breast cancer in adults. Recursive partitioning analysis was performed to group patients with similar overall survival (OS) based on clinical T/N stage, tumor grade, ER, PR, HER2, number of metastatic locations, and presence of bone-only metastases; they performed recursive partitioning analysis to group patients with similar OS. Stage IVA: more than 50%, stage IVB: 30%–50%, and stage IVC: less than 30% were constructed by combining homogeneous groups based on 3-year OS rates. There were 16,187 individuals identified, with a median follow-up of 32 months. About 65.2% of patients had at least 1 distant metastatic site, while 42.9% had solely bone metastases. For both groups, recursive partitioning analysis identified the first stratification point as the number of metastatic sites (1 vs >1) and the second stratification point as the ER status. The study group formed additional classifications based on bone-only metastases, HER2 status, PR status, CT stage, tumor grade, and HER2 status. Significant differences in 3-year OS between the 3 groups were found after bootstrapping [stage IVB vs IVA: HR 1.58 (95% CI 1.50–1.67), stage IVC vs IVA: HR 3.54 (95% CI 3.33–3.77)]. In patients with metastatic illness, morphological and biologic criteria provided reliable and repeatable prognostic estimations. The data support the classification of stage IV de novo breast cancer into 3 separate prognostic groups.
