Matrix-producing metaplastic breast carcinoma - a rare tumor with heterologous elements.

Metaplastic breast carcinomas are ductal carcinomas that undergo metaplasia into non-glandular growth patterns. They are very rare and account for less than 1% of all invasive breast carcinomas. Matrix-producing carcinoma is an extremely rare and aggressive subtype of metaplastic breast carcinoma that is characterized by a ductal carcinomatous component with direct transition to areas with cartilaginous/osseous differentiation without an intervening spindle cell element. It has a better prognosis than metaplastic carcinoma. Even though these tumors are composed of a mixture of infiltrating ductal carcinomas and areas of heterologous stroma, each of which behaves aggressively individually, these composite tumors have a better 5-year survival rate with rare nodal metastasis. Immunohistochemically, they are positive for keratin, epithelial membrane antigen and S100. The tumor, which is matrix-producing, is S100-reactive and nonreactive for cytokeratin. They are usually hormone receptor-negative. The average age of these patients is approximately 58 years. Since these tumors are usually triple-negative, chemotherapy after surgery is the mainstay of therapy, using either mastectomy or local excision. Our report highlights this rare entity in a 55-year-old female patient with matrix-producing metaplastic breast carcinoma. Its distinctive histological features and peculiar clinical behavior warrants clear knowledge about this unique entity.