The Molecular Subtype Dependent Effect of Concurrent Radiotherapy and Systemic Therapy on Breast Cancer: Analysis of a Human In Vivo Model of Metastatic Brain Lesions

ABSTRACT

PURPOSE: The molecular subtype of breast cancer is an important predictive factor. Therefore, we investigated the effects of concurrent or serial radiotherapy and systemic therapy on metastatic brain lesions according to the molecular subtype of breast cancer. METHODS: The present retrospective study examined data from 66 patients with breast cancer and metastatic brain lesions, who were treated using radiotherapy between January 1990 and July 2014. Patients were classified into the following three subtypes based on their hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status HR+/HER2− (luminal A, 13 patients), HR+/HER2+ (luminal B, 21 patients), HR−/HER2+ (HER2, 22 patients), or HR−/HER2− (triple negative, 10 patients). The brain lesions and their responses to treatment were evaluated using brain computed tomography or magnetic resonance imaging. Progression of brain disease was defined by a ≥20% increase in the sum of the lesion's diameters or the development of a new brain lesion. Progression-free survival was calculated from the initiation of radiotherapy to the first instance of brain disease progression or last follow-up. RESULTS: Patients in the HER2 group who had received concur-rent radiotherapy and systemic therapy (mainly HER2-targeted therapy) exhibited significantly better progression-free survival than did patients who had received radiotherapy followed by systemic therapy (p=0.037). However, concurrent radiotherapy and systemic therapy did not significantly improve progression-free survival in the luminal A (p=0.527), luminal B (p=0.462), or triple negative (p=0.558) groups. CONCLUSION: Concurrent radiotherapy and mainly HER2-targeted systemic therapy significantly prolonged progression-free survival in the HER2 group.