Metaplastic carcinoma of the breast with mesenchymal differentiation (carcinosarcoma). A unique presentation of an aggressive malignancy and literature review.

Metaplastic carcinoma of the breast with mesenchymal differentiation (MCMD), previously known as carcinosarcoma, is a very rare and aggressive tumor that has been recently 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. Histologically, MCMD is characterized by a biphasic pattern of malignant epithelial and sarcomatous components without evidence of a transition zone between the two elements. We herein describe a unique case of metaplastic carcinoma of the breast with chondrosarcomatous differentiation in a postmenopausal woman who presented with a large, rapidly growing, ulcerated, bleeding mass and signs of impending sepsis. Metaplastic breast carcinomas (MBC) are rare and aggressive tumors. They are characterized by larger size, lower rates of axillary node involvement, higher rates of triple negativity and distal metastases, earlier local recurrence and poorer survival compared with classic invasive breast cancer. Because of the rarity of MBC, the optimal treatment has not been well defined. Surgery is the main curative treatment modality since MBC has shown a suboptimal response to standard chemotherapy. Patients with MBC may be appropriate candidates for novel targeted therapies.