Fine-needle aspiration cytology of sarcomatoid carcinoma of the breast: a cytologically overlooked neoplasm.

Sarcomatoid carcinoma of the breast is a very uncommon neoplasm. Fine-needle aspiration findings have been rarely reported. We report a case of sarcomatoid carcinoma of the breast that was diagnosed as a typical ductal carcinoma cytologically. The patient was a 45-year-old female who had a right breast mass for a short duration. Fine-needle aspiration (FNA) showed smears predominantly composed of single cells exhibiting plasmacytoid features with moderate degree of pleomorphism. A granular bluish background was noted on the Papanicolaou-stained smears. This background was thought to represent tumor diathesis, and the diagnosis of grade II ductal carcinoma of the breast was rendered. The patient underwent a subsequent lumpectomy with axillary node dissection. Histological examination of the lumpectomy revealed a neoplasm predominantly composed of a grade II chondrosarcoma with increased cellularity. A small (10%) component showed grade II invasive ductal carcinoma of the breast. No in situ component was seen. The sarcomatoid component was positive for S-100 protein and vimentin and negative for keratin, whereas the carcinomatous component was positive for vimentin, epithelial membrane antigen, and low molecular weight keratin. Ultrastructurally, the tumor showed features of a poorly differentiated epithelial neoplasm without evidence of chondrosarcoma. Metastases were seen in seven of ten axillary lymph nodes with exclusive epithelial component. Retrospective evaluation of the FNA smears revealed an extensive metachromatic stroma of the DIFF QUIK-stained smears. Our findings and review of the literature suggest that sarcomatoid carcinoma of the breast will be very frequently overlooked or misdiagnosed either because of the subtlety of the stroma or the predominance of the mesenchymal component. Our findings also provide supportive evidence that the use of the DIFF QUIK stain can be very helpful in the identification of the stroma in this neoplasm. The predominance of epithelium in the metastases in our case is further proof that tumors with dual differentiation such as sarcomatoid carcinomas and mixed muellerian tumors are truly carcinomas with metaplastic features.