Rates of brain metastases and association with breast cancer subtypes in Ontario, Canada

Approximately 1 in 7 patients with metastatic breast cancer (MBC) will receive radiotherapy for brain metastases (BMs). Significant differences in cumulative incidence of BMs by breast cancer subtype may inform future BM screening protocols. A population-based retrospective cohort study in Ontario (Canada) found that among patients with de novo MBC the cumulative incidence of BMs was higher among patients with HER2-positive/HR-negative disease (34.7%), HER2-positive/HR-positive disease (28.1%), and triple-negative disease (21.9%), than among patients with HER2-negative/HR-positive disease (12.1%). The median time from MBC diagnosis to brain radiotherapy ranged from 7.5 months (IQR 2.3-17.4) for patients with TNBC to 19.8 months (IQR 12.2-35.1) for those with HER2-positive/HR-positive disease.