Matrix-producing carcinoma of the breast in the Chinese population: a clinicopathological study of 13 cases.

Matrix-producing carcinoma (MPC) of the breast is an extremely rare variant of metaplastic carcinoma. The aim of this study was to evaluate the clinicopathological features and immunohistochemical expression profile of this rare tumor in Chinese population. Thirteen cases of MPC were evaluated using morphology observation and immunohistochemistry. All tumors had invasive carcinoma with an abrupt transition to chondromyxoid matrix without an intervening spindle cell sarcomatoid component. The distribution of tumor cells was diffuse in eight cases and peripheral in five cases. Matrix distribution was diffuse or multifocal. Necrosis was present in 11 cases. An overt invasive ductal carcinoma was observed in 11 cases and the other two tumors were consistent with MPC arising in microglandular adenosis. Ten of 13 cases were triple negative (ER-, PR-, Her2/neu-). Eight of 10 triple negative cases were cytokeratin 5/6, cytokeratin 14 or epidermal growth factor receptor positive, consistent with the basal-like phenotype. S-100 protein was positive in all cases. At the time of initial diagnosis, one of 13 patients had lung metastasis and axillary lymph nodes metastasis. Follow-up time ranged from 6 to 30 months. All patients remained alive. One patient developed a soft tissue metastasis 24 months after surgery.