A case of positive mixed epithelial/mesenchymal metaplastic breast carcinoma (carcinosarcoma). Towards novel therapeutic targets: case report.

Background: Metaplastic breast cancer (MeBC) is a rare malignancy, representing less than 1% of all breast cancers. We present a case of triple-negative MeBC with a biphasic growth pattern, including malignant mesenchymal and epithelial components.

Case report: A 45-year-old female patient presented to our hospital with a 1-month history of a lump in her right breast. Upon clinical examination, a mass measuring 24 mm in diameter was revealed at 10-11 o'clock in the outer upper quadrant of the right breast. The patient was submitted for ultrasound scanning, ultrasound-guided core needle biopsy, and excisional biopsy which revealed a mixed epithelial/mesenchymal tumor, 8 cm in diameter. A complete immunohistochemical profile was presented. A right modified radical mastectomy with axillary lymph node dissection was performed and was tolerated well by the patient. The histological diagnosis of the lesion was MeBC with the epithelial component consistent with a grade 3 ductal adenocarcinoma. The 14 dissected axillary nodes were not involved. The patient was later submitted for adjuvant chemotherapy and radiotherapy. To date, 24 months postoperatively, the patient remains without any signs or symptoms of residual disease or recurrence.

Conclusion: The aggressive behavior and chemoresistance of MeBC warrants early diagnosis and treatment to achieve optimal outcome.