Background Patients with metastatic breast cancer (MBC) are living longer, but development of brain metastases often limits their survival. We conducted a systematic review and meta-analysis to determine the incidence of brain metastases in this patient population. Methods Articles published from January 2000 to January 2020 were compiled from four databases using search terms related to: breast cancer, brain metastasis, and incidence. The overall and per patient-year incidence of brain metastases were extracted from studies including patients with HER2+, triple negative, and hormone receptor (HR)+/HER2- MBC; pooled overall estimates for incidence were calculated using random effects models. Results 937 articles were compiled, and 25 were included in the meta-analysis. Incidence of brain metastases in patients with HER2+ MBC, triple negative MBC, and HR+/HER2- MBC was reported in 17, 6, and 4 studies, respectively. The pooled cumulative incidence of brain metastases was 31% for the HER2+ subgroup (median follow-up: 30.7 months, IQR: 24.0 – 34.0), 32% for the triple negative subgroup (median follow-up: 32.8 months, IQR: 18.5 – 40.6), and 15% among patients with HR+/HER2- MBC (median follow-up: 33.0 months, IQR: 31.9 – 36.2). The corresponding incidences per patient-year were 0.13 (95% CI: 0.10 – 0.16) for the HER2+ subgroup, 0.13 (95%CI: 0.09 – 0.20) for the triple negative subgroup, and only 0.05 (95%CI: 0.03 – 0.08) for patients with HR+/HER2- MBC. Conclusion There is high incidence of brain metastases among patients with HER2+ and triple negative MBC. The utility of a brain metastases screening program warrants investigation in these populations.

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