Brain metastasis risk model externally validated in stage I–III breast cancer

Researchers developed the Brain Metastasis Risk (BrMR) model to estimate brain metastasis risk in patients with stage I–III breast cancer. The retrospective training cohort included 40,282 patients diagnosed at MD Anderson Cancer Center between 1997 and 2020. After data curation and multiple imputation of missing values, the model was implemented as an online calculator and tested in an independent cohort of 1,644 patients referred to Institut Jules Bordet, Belgium, between 2001 and 2021.

Brain metastases occurred in 2,408 training-cohort patients and 35 validation-cohort patients. The C-index was 0.79 in training and 0.76 in validation. Reported areas under the receiver operating characteristic curve were 0.81, 0.79, 0.76, and 0.75 at 4, 6, 8, and 10 years, respectively. Features associated with higher risk included inflammatory breast cancer, HER2 positivity, higher Ki-67, lymphovascular invasion, grade III, higher T/N-status, and adjuvant chemotherapy. ER/PR positivity, older age, endocrine therapy, and lobular histology were among factors associated with lower risk.

The model could support risk stratification and clinical trial enrichment, but these observational associations do not establish causal effects of treatment. The external cohort had only 35 brain metastasis events, and the supplied abstract does not report calibration results. Prospective validation is needed before using BrMR to guide surveillance; the study does not establish that calculator-guided surveillance improves outcomes.