ABSTRACT
<p><b>OBJECTIVE</b>To study the clinicopathologic features, immunophenotype and prognosis of matrix-producing metaplastic carcinoma (MPC).</p><p><b>METHODS</b>Sixteen cases of MPC diagnosed between 2002 and 2012 in West China Hospital were identified. The clinicopathologic features were analyzed. Immunohistochemistry for E-cadherin, S-100 protein, CK5/6, HCK, PCK, CK7, CK8, p63, SMA, EMA, CD99, MSA, CK14, EGFR, ER, PR, HER2 and Ki-67 was performed with EnVision method. The clinical outcome was evaluated and compared to matched controls of invasive ductal carcinoma.</p><p><b>RESULTS</b>All patients were women and ranged in age from 29 to 69 years (median age 48 years). The median size of primary tumor was 4 cm. Most of the tumors were well-circumscribed with expansile and multinodular appearance. Histology showed invasive carcinoma with a direct transition from carcinoma to cartilaginous/chondromyxoid matrix without an intervening spindle cell component. Tumor distribution was either nodular or diffuse. The matrix component accounted for 10%-80% of the tumor volume. All the tumors were strongly positive for S-100 protein and basal-like cytokeratin with triple negative phenotype (ER, PR and HER2 negative). Alcian blue stain was positive for the cartilaginous/chondromyxoid matrix. Compared with invasive ductal carcinoma, patients with MPC had increased locoregional recurrence (P = 0.010), increased distant recurrence (P = 0.011) and shorter disease-free survival (P = 0.017).</p><p><b>CONCLUSIONS</b>MPC is a rare variant of mammary metaplastic carcinoma with unique characteristics of morphology and immunohistochemical staining pattern. This subtype seems to have aggressive biologic behavior.</p>