The significance of atypical apocrine cells in fine-needle aspirates of the breast.

Apocrine metaplastic cells are frequently present in fine-needle aspirates (FNAs) of breast lesions, especially fibrocystic disease. Occasionally, apocrine cells may be atypical and present diagnostic difficulties. The morphologic features of six breast FNAs that contained atypical apocrine cells in breast aspirates. In the six abnormal cases, the large, pleomorphic, atypical apocrine cells were the predominant cell type and occurred singly and in syncytial tissue fragments. The cells had large, eccentric, vesicular nuclei and usually multiple macronucleoli. The histologic diagnoses in the cases were apocrine carcinoma (five cases) and atypical apocrine metaplasia (one case). In comparison, benign apocrine cells are relatively small and uniform and arranged in cohesive, orderly sheets. It is concluded that, in breast FNAs, the predominance of atypical apocrine cells, occurring singly and in syncytia, should raise the suspicion of carcinoma.