OBJECTIVETo study the clinicopathologic features, immunophenotype and prognosis of matrix-producing metaplastic carcinoma (MPC).

METHODSSixteen 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.

RESULTSAll 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).

CONCLUSIONSMPC 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.