Survival Outcomes of Metaplastic Breast Cancer Patients: Results from a US Population-based Analysis

Background Metaplastic breast cancer (MBC) is a rare histologic subtype needing further characterization. The aim of our study was to compare MBC to infiltrating ductal carcinoma (IDC) of the breast and to identify demographic, clinicopathologic, treatment, and survival differences. Methods MBC and IDC patients were identified using the Surveillance, Epidemiology, and End Results (SEER) public-use data set. Disease-specific survival (DSS) differences were compared using the Kaplan–Meier method and log-rank tests. Univariate and multivariate Cox proportional hazard models were used to assess factors prognostic for DSS. To control for hormone receptor status, a subsequent planned analysis was completed for receptor-negative MBC and IDC. Lastly, a matched case-control analysis was conducted to minimize potential bias due to baseline demographic, clinical, and pathologic differences. Results The SEER data set included 1,011 MBC and 253,818 IDC patients diagnosed from 2001 to 2010. MBC patients had larger, higher grade tumors, had less frequent axillary nodal involvement, and were more likely to be treated with mastectomy. Five-year DSS rates were significantly worse for patients with MBC than for IDC patients (78 vs. 93 %, p