Matrix-producing carcinoma (MPC) of the breast is a subtype of metaplastic carcinoma defined as an invasive breast carcinoma with a direct transition of carcinoma to cartilaginous or osseous matrix without an intervening spindle cell component. Our aims were (1) to evaluate specific histologic characteristics of MPC and correlate these with disease recurrence; and (2) to determine whether rates of locoregional and distant recurrence for MPC are significantly different from those of invasive ductal carcinoma. Thirty-two cases of MPC were identified. Fourteen patients (44%) were < or =50 years of age; 10 (31%) had tumors of size < or =2 cm, and 6 (19%) had tumors > or =5 cm. In this series, all tumors contained chondromyxoid or chondroid matrix, and 1 (3.1%) also contained focal (<5%) osseous matrix. High-grade matrix was present in 9 cases (28%), and low-grade matrix was present in 23 (72%). Matrix comprised < or =10% of the tumor in 14 cases (44%), >10% but <40% in 9 (28%), and > or =40% in 9 (28%). The carcinomatous component was high grade in 30 cases (94%), and 19 tumors (59%) had central necrosis. Seven patients (22%) had positive axillary lymph nodes, and 8 (25%) had lymphovascular space invasion (LVSI). LVSI was the only factor independently associated with locoregional recurrence-free survival in multivariate analysis (P=0.043). Although > or =40% matrix was associated with improved distant recurrence-free (DFS) survival in univariate analysis (P=0.044), only LVSI and tumor stage were independently associated with DFS survival in multivariate analysis (P=0.027 and P=0.001, respectively). Compared with matched controls with invasive ductal carcinoma, patients with MPC had decreased locoregional recurrence-free survival (P=0.001) and decreased DRF survival (P=0.001). In summary, MPC is an aggressive subtype of metaplastic carcinoma with a worse clinical outcome than invasive ductal carcinoma.