Fine-needle aspiration cytology of solid papillary carcinoma of the breast

We report a case of solid papillary carcinoma (SPC) of the breast, of which the cytologic findings of the nipple discharge and the fine needle aspiration (FNA), and the pathology of the resected tumour are described in detail. Imaging studies demonstrated an intra-ductal tumour of the breast, which seemed responsible for the bloody nipple discharge. The cytologic features of the nipple discharge and the FNA targeted to the intra-ductal tumour suggested low-grade carcinoma. Additional findings of mucin production and rosette-formation (possibly neuroendocrine differentiation) indicated SPC as a major differential diagnosis. Histologically, the lesion consisted of mainly ductal proliferation of low-grade carcinoma associated with prominent rosette formation within the tumour and mucin production. Permeation of mucin with cancer cell clusters into the adjacent adipose tissue was also noted. Immunohistochemically, the tumour cells, especially those forming rosettes, were partially positive for CD56. Histological diagnosis was SPC with invasion. SPC is a rare tumour, and its cytologic and pathologic features have only been sporadically reported. Our case was unique in that there was a good correlation between cytologic and histologic findings. The cytologic findings that are important to predict the histologic diagnosis are emphasized. A brief review of the relevant literature is also included.