Prevalence by therapy line and incidence of breast cancer brain metastases in 18 075 patients

Abstract

IMPORTANCE: Brain metastases portend poor prognosis in patients with metastatic breast cancer (MBC). Designing treatment and prevention clinical trials requires knowledge of brain metastases incidence with each line of therapy. OBJECTIVES: We assessed the prevalence and cumulative incidence of brain metastases in a large MBC patient cohort by subtype and line of therapy, and the impact of HER2-low expression on prevalence. DESIGN, SETTING AND OUTCOMES: We analyzed brain metastases prevalence in patients with MBC in a nationwide electronic health record-derived de-identified database. The primary outcome was first diagnosis of brain metastases. We estimated prevalence and incidence of brain metastases by MBC subtype, including HER2-low and therapy line. We used the cumulative incidence function to estimate brain metastases risk in patients without brain metastases at initiation of systemic therapy. All P-values are 2-sided, and a P-value ≤.05 indicates statistical significance. RESULTS: Among 18 075 patients with MBC, 1102 (6.1%) had at least 1 brain metastasis at first-line therapy initiation. For the remaining 16 973 patients, cumulative incidence of brain metastases at 60 months was 10% in patients with hormone receptor-positive (HR+)/HER2- disease, 23% for HR+/HER2+ disease, 34% for HR-/HER2+ disease, and 22% for triple-negative breast cancer (TNBC). HER2-low expression within HR+/HER2- and TNBC subtypes had no impact on brain metastases incidence. Brain metastases prevalence increased per line of therapy for patients with all breast cancer subtypes. CONCLUSIONS: Brain metastases incidence increases per line of therapy for every MBC subtype. The HER2-low biomarker does not impact brain metastases incidence within historical subtypes.