Metaplastic carcinoma of the breast with mesenchymal differentiation: a rare case report and literature review

Metaplastic breast carcinoma with mesenchymal differentiation (MCMD), formerly known as carcinosarcoma, is a very rare and aggressive tumor that has recently been classified as a subtype of metaplastic breast carcinoma. It accounts for 0.08%–0.2% of all breast cancers, with only a few cases reported in the literature. Here we report a case of a 56-year-old woman with a large, hard lump in her right breast, with no history of breast cancer in first degree relatives. Symptoms were present 6 months before presentation. After hospitalization and following physical evaluation, USG, mammography, biopsy and immunohistochemistry, the diagnosis of metaplastic carcinoma with mesenchymal differentiation was established. Two of 11 axillary lymph nodes were positive for metastases. The optimal treatment modality for metaplastic carcinoma is not yet established due to its rarity and heterogeneity. Modified radical mastectomy is the preferred surgical procedure because a large tumor size is a contraindication for breast conserving surgery. In conclusion, a patient with such an enlargement of the breast mass must be carefully evaluated, for the correct diagnosis of a possible metaplastic carcinoma.