A Rare Case of Primary Carcinosarcoma of the Breast

Abstract Breast carcinosarcoma is a rare malignancy accounting for approximately 0.08–0.2% of all breast tumours. It is a type of metaplastic mammary carcinoma displaying biphasic differentiation with epithelial and mesenchymal cellular characteristics with probable derivation from myoepithelial cells. A 65-year-old woman presented to our hospital with a two-month history of a rapidly growing mass in her left breast. Neither her medical nor family history was positive for malignancies. Subsequently, she underwent a fine needle aspiration, which was positive for adenocarcinoma, followed by a lumpectomy with axillary lymph node dissection. The histology revealed an undifferentiated neoplasm and the immunohistochemical cell staining was positive for pan-cytokeratin, SMA, Vimentin, and S-100, suggesting the diagnosis of breast carcinosarcoma with a triple-negative immunophenotype. There was no evidence of metastasis except for a positive lymph node, indicating a stage IIIA disease. Thus, she received adjuvant chemo-radiotherapy. However, 16 months later, she presented with metastatic disease, and unfortunately, she died 4 months later due to a systemic infection. Aggressive behavior, higher staging, chemoresistance, and higher proportion of triple negative breast cancer seem to be the main characteristics of breast carcinosarcoma, which is recognised as a separate entity from common invasive ductal carcinoma, with significantly worse clinical outcomes.