Matrix-producing carcinoma of the breast: a case report.

Matrix-producing breast cancer (MPC) is a subtype of metaplastic carcinoma of the breast. It is a very rare tumor, which constitutes less than 1% of all malignant mammary tumors. The origin of this tumor is still unclear: there are molecular studies that suggest an origin from myoepithelial cells, whereas other studies underline the neoplastic transformation of a multipotent stem cell. Even the differential diagnosis of MPC and other breast neoplasms (phyllodes tumors and real sarcomas of the breast) is not always easy. In the literature, a certain chemoresistance has been demonstrated, and a standard treatment of this tumor does not exist at this time. We report the case of a 44-year-old, premenopausal, female patient with a 6-cm breast lump. Neither imaging nor fine needle aspiration biopsy was crucial in achieving a diagnosis. The patient underwent a simple mastectomy. In consideration of the negative lymph node status, the patient was not subjected to radiotherapy or adjuvant chemotherapy. Moreover, since the receptor status was negative, hormone therapy was not necessary. The patient has been disease free for 4 years now.