Summary of the results from the recursive partitioning analysis into the fewest groups, while still maintaining the final overall prognostic stage group (A/B/C). Results based on adults with de novo metastatic breast cancer from the National Cancer Data Base (2010–2013). S indicates number of metastatic sites, G indicates grade. Black boxes represent decision points, while white and gray boxes represent potential outcomes for the decision. Gray boxes also represent terminal nodes with the final stage grouping (A/B/C). ER indicates estrogen receptor; HER2, human epidermal growth factor receptor 2; PR, progesterone receptor.