Timing and prognosis of brain metastasis development in breast cancer by subtype.

Limited data on the timing of brain metastases development and subsequent prognosis by breast cancer subtype exist. We retrospectively evaluated a cohort of 671 patients diagnosed with brain metastases secondary to breast cancer. Patients were categorized by subtype: human epidermal growth factor receptor 2-positive (HER2+), hormone receptor-positive/HER2-negative (HR+/HER2-), and triple negative (TN). We found significant heterogeneity in the timing of brain metastases development and subsequent prognosis by subtype. Patients with HR+/HER2- disease developed brain metastases later in the disease course compared to patients with HER2+ and TN disease. Median overall survival following brain metastases diagnosis was shortest in patients with TN disease; however, among all subtypes, overall survival decreased with an increasing number of systemic therapies prior to the diagnosis of brain metastases. Altogether, these findings may inform differential timing of brain-directed screening imaging in patients with breast cancer.