Association of recurrence patterns and outcome with <scp>HR</scp> and <scp>HER2</scp> status in patients with resected brain metastases from breast cancer

Advanced breast cancer is associated with the development of brain metastases in 20%-40% of patients. Differential post-radiotherapy recurrence patterns depending on hormone receptor (HR) and human epidermal growth receptor 2 (HER2) status have been reported. We investigated recurrence patterns after microsurgical resection stratified for HR and HER2 expression. The institutional database was screened for patients who had undergone tumor resection for breast cancer brain metastases between 2013 and 2023. Patient and imaging data were analyzed. Response Assessment in Neuro-Oncology (RANO) guidelines were applied. Sixty-seven patients were identified. Nineteen patients (28%) were diagnosed with HR+/HER2-, 31 patients (46%) with HER2+, and 17 patients (25%) with triple-negative (TN) brain metastases. Local, i.e., in or adjacent to the resection cavity, or distant brain-specific progression-free survival (PFS) was shortest in patients with TN status, followed by patients with HER2+ and HR+/HER2- brain metastases (median: 170 vs. 419 vs. 1152 days; p < .01). Patients with HER2+ brain metastases showed earlier local progression than patients with HR+/HER2- status (HR 0.25; 95% CI 0.08-0.75; p = .01). The receptor status of the brain metastases diverged from the primary tumor in 13 patients (21%). In five patients (8%), a newly gained HR or HER2 expression was detected. Post-surgery recurrence patterns of breast cancer brain metastases are associated with the tumor biology. TN brain metastases show earliest local and distant recurrence, confirming the pressing need for better local and systemic treatments. As HER2+ brain metastases tend to recur locally, refinement of local strategies might be warranted.