Clinical outcomes and a nomogram for de novo metastatic breast cancer with lung metastasis: a population-based study.

To better understand the clinical characteristics of newly diagnosed lung metastatic breast cancer (LMBC) and quantify its prognosis, we retrieved data on patients with LMBC from the Surveillance, Epidemiology, and End Results database. Eligible patients were randomly assigned to training and validation cohorts (ratio 7:3) to establish a nomogram using the Cox proportional hazards regression model. In total, 4310 patients with LMBC were enrolled, including 52.4% (2259/4310) HR+/HER2-, 17.6% (757/4310) HR+/HER2+, 10.8% (467/4310) HR-/HER2+, and 19.2% (827/4310) HR-/HER2- subtype patients. Inclinations of lung and brain involvement in HR-/HER2+ and HR-/HER2- subgroups, liver involvement in the HER2 overexpressing subgroup, and bone involvement in the HR-positive subgroup were detected in the LMBC population. Regarding prognosis, HR+/HER2+ subtype patients presented the most favorable profile (mOS 35.0 months, 95% CI 30.1-39.9), while HR-/HER2- patients exhibited the worst (mOS 11.0 months, 95% CI, 10.0-11.9). A nomogram was developed in the training cohort and validated internally (C-index 0.70) and externally (C-index 0.71), suggestive of decent performance. This study assessed the clinical outcomes associated with molecular subtypes, metastatic patterns, and surgical intervention and provided a robust nomogram for the estimation of survival probabilities, which are promising for the management of LMBC in clinical practice.