RESUMO
Matrix-producing carcinoma of the breast is very rare with few cases reported in the literature. This entity is characterized by the association of malignant epithelial elements and a mesenchymal component. Therapeutic strategy is not well established and prognostic factors need further research. We report here a case of matrix-producing carcinoma in a 46-years-old woman who presented with a large lump in her left breast. A core biopsy concluded to an invasive carcinoma but neoadjuvant chemotherapy was not helpful. Diagnosis of matrix-producing carcinoma was done on the lumpectomy specimen after excision of the fast-growing mass. Immunophenotypic profile was very suggestive showing tumoral cells positivity for cytokeratins, epithelial membran antigen and S-100 protein. One year later, the patient developed lung metastases.