MLTI-16. SYSTEMIC THERAPY FOLLOWING CRANIOTOMY IN PATIENTS WITH A SOLITARY BREAST CANCER BRAIN METASTASIS

INTRODUCTION: Between 15–50% of patients with metastatic breast cancer will develop brain metastases, with the frequency more common in patients with HER2-positive or triple-negative subtypes. Surgical resection is often indicated for diagnostic and/or therapeutic intent for patients presenting with a solitary lesion and/or symptomatic lesion(s) with mass effect. Practice patterns and patient outcomes with respect to the use of postoperative systemic therapy (ST) after resection of a solitary breast cancer brain metastasis (BCBM) have not been previously well-described, particularly in the modern era. METHODS: A multi-institutional retrospective review of 44 patients was performed to assess the impact of types of ST on site of recurrence, progression-free survival (PFS) and overall survival (OS) after resection of solitary BCBM. RESULTS: Stratified estimated survival was 15, 24 and 23 months for patients with triple negative, estrogen receptor positive (ER+), and human epidermal growth factor receptor 2 positive (HER2+) BCBMs. Patients receiving postoperative ST had a longer median PFS (8 versus 4 months) and OS (32 versus 15 months). Nine patients (20%) had extracranial progression, 23 (52%) had intracranial progression, three (8%) had both, and nine (20%) did not experience progression at last follow-up. Multivariate analysis showed that postoperative hormonal therapy was associated with longer OS in estrogen receptor (ER) positive patients (HR = 0.26; CI = 0.08 – 0.89; p = 0.03), but not with longer PFS. Postoperative human epidermal growth factor receptor 2 (HER2)-targeted therapy was not associated with longer PFS or OS in HER2+ patients. CONCLUSIONS: Disease progression occurred intracranially more often than extracranially following resection of a solitary BCBM. In ER+ patients, postoperative hormonal therapy was associated with longer OS. Postoperative HER2-targeted therapy did not show survival benefits in HER2+ patients. These results should be validated in larger cohorts.