[Breast cytopathology. Diagnostic difficulties and limits]

Diagnostic difficulties can arise during the cytologic diagnosis of almost all types of breast lesions. "True" difficulties, which are discussed herein, should be differentiated from difficulties due to faulty technique. The frequency of diagnostic difficulties varies across lesions: the proportion of "suspicious" specimens is 4% in adenofibroma, 5 to 7% in cancer, and 17% in epithelial duct hyperplasia, and the false-negative rate in cancer is 3 to 5%. Many difficulties can be overcome by a good knowledge of breast cytopathology. Others are insuperable and should remain so to avoid diagnostic mistakes. In these cases, which should be considered "suspicious", the clearly written documented report should request a histological study. The distinction between duct carcinoma and lobular carcinoma remains difficult, and that between invasive carcinoma and intraductal carcinoma requires a histologic study.