Association between contralateral background parenchymal enhancement on MRI and outcome in patients with unilateral invasive breast cancer receiving neoadjuvant chemotherapy

The purpose of this study was to retrospectively investigate whether background parenchymal enhancement (BPE) of the contralateral breast on magnetic resonance imaging (MRI) is associated with clinical outcomes in patients with unilateral invasive breast cancer receiving neoadjuvant chemotherapy (NAC).A total of 228 women (47.6 years ± 10 [SD]; range: 24-74 years) with invasive breast cancer who underwent NAC between 2005 and 2013 were included. All included patients underwent breast MRI before and after NAC. Quantitative semiautomated analysis of BPE of the contralateral healthy breast was performed. The enhancement level on baseline MRI (baseline BPE) and on MRI after chemotherapy (final BPE) and the change in enhancement rate between baseline MRI and final MRI were recorded. Cox regression was used to test associations between BPE variables, patient and tumor characteristics, overall survival (OS) and disease-free survival (DFS). Subgroup analyses based on menopausal status and immunohistochemical subtypes were performed.Median follow-up was 92 months. Multivariable analysis revealed that Ki-67 level (P = 0.026) and receipt of mastectomy (P = 0.015) were independent variables associated with OS while Ki-67 level (P = 0.010) and post-NAC pathological node categorization (P = 0.027) were independent variables associated with DFS. BPE was not associated with OS (P = 0.500, 0.546 and 0.712 for baseline BPE, final BPE and BPE change, respectively) or with DFS (P = 0.568, 0.412 and 0.327, respectively).BPE of the contralateral breast on MRI may have limited prognostic value in patients with breast cancer treated with NAC.