Background: Metaplastic breast carcinomas are ductal carcinomas that undergo metaplasia into non-glandular growth patterns. They are very rare, accounting for less than 1% of all invasive breast carcinomas.
Case Report: A 33-year-old female patient presented with a lump in her left breast. Axillary lymph nodes were not palpable. FNAC of the lump was positive for malignant cells. The patient underwent modified radical mastectomy with axillary clearance. The histopathological report was matrix-producing carcinoma with infiltrating duct carcinoma. The tumor was positive for immunohistochemical markers keratin, EMA (Epithelial Membrane Antigen), and S100, thus confirming it to be matrix-producing carcinoma breast. After surgery, the patient recovered uneventfully.
Conclusions: Matrix-producing breast carcinoma is a rare type of metaplastic carcinoma characterized by a ductal carcinomatous element with direct extension to areas showing cartilaginous or osseous differentiation, lacking an interspersed spindle cell component. It has better prognosis than metaplastic carcinoma.
Immunohistochemically, they are positive for keratin, EMA (Epithelial Membrane Antigen), and S100. The tumor, which is matrix-producing, is S100 reactive and nonreactive for cytokeratin. They are usually ER- and PR-negative. The average age of these patients is approximately 58 years. Surgery remains the mainstay of therapy, using either mastectomy or local excision.

Keywords: matrix producing, breast carcinoma, metaplastic