Apocrine adenosis is a distinctive breast lesion, which can sometimes be misdiagnosed as malignant histologically. Although its histological characteristics have been well established, there are limited descriptions of its cytological features. We report fine-needle aspiration (FNA) cytology of three cases of apocrine adenosis. There were diverse cytological features between cases, and in two cases, FNA smears were highly cellular. Naked nuclei were present in all cases, and were numerous in one. Enlarged nucleoli and anisonucleosis were common. Apocrine metaplasia with nuclear atypia mimicking apocrine carcinoma was prominent in one case, whereas one case lacked definite apocrine features. Regardless of their various atypical FNA cytologies, the nuclei were consistently less hyperchromatic in all cases. Although FNA cytology of apocrine adenosis has the potential to be misinterpreted as malignant, the naked nuclei of background and less hyperchromatic nuclear features may be useful in distinguishing apocrine adenosis from carcinoma. Being familiar with these distinctive breast lesions is also important in decreasing false positives.
(c) 2007 Wiley-Liss, Inc.