Hormone receptors status: a strong determinant of the kinetics of brain metastases occurrence compared with HER2 status in breast cancer

Breast cancer (BC) metastatic behavior varies according to the hormone receptors (HR) and HER2 statuses. Indeed, patients with triple-negative (TN) and HER2+ tumors are at higher risk of brain metastases (BM). The objective of this multinational cohort was to evaluate BM kinetics depending on the BC subtype. We retrospectively analyzed a series of BC patients with BM diagnosed in four European institutions (1996-2016). The delay between BC and BM diagnoses (BM-free survival) according to tumor biology was estimated with the Kaplan-Meier method. A multivariate analysis was performed using the Cox proportional hazards regression model. 649 women were included: 32.0% HER2-/HR+, 24.8% TN, 22.2% HER2+/HR- and 21.0% HER2+/HR+ tumors. Median age at BM diagnosis was 56 (25-85). In univariate analysis, BM-free survival differed depending on tumor biology: HER2-/HR+ 5.3 years (95% CI 4.6-5.9), HER2+/HR+ 4.4 years (95% CI 3.4-5.2), HER2+/HR- 2.6 years (95% CI 2.2-3.1) and TN 2.2 years (95% CI 1.9-2.7) (p < 0.001). It was significantly different between HR+ and HR- tumors (5.0 vs. 2.5 years, p < 0.001), and between HER2+ and HER2- tumors (3.2 vs. 3.8 years, p = 0.039). In multivariate analysis, estrogen-receptors (ER) and progesterone-receptors (PR) negativity, but not HER2 status, were independently associated with BM-free survival (hazard ratio = 1.36 for ER, p = 0.013, 1.31 for PR, p = 0.021, and 1.01 for HER2+ vs. HER2- tumors, p = 0.880). HR- and HER2+ tumors are overrepresented in BC patients with BM, supporting a higher risk of BM in these biological subtypes. HR status, but not HER2 status, impacts the kinetics of BM occurrence.