Fine-needle aspiration cytology of mammary adenomyoepithelioma: A study of 12 patients

BACKGROUND. Adenomyoepithelioma (AME) of the breast is a rare neoplasm that is characterized by a biphasic proliferation of epithelial and myoepithelial cells. Incomplete excision of this lesion is associated with a greater risk of recurrence. Although the histology of AME is well characterized, its cytomorphology has not been assessed in a large series. METHODS. The authors conducted a retrospective evaluation of cytologic findings in fine-needle aspiration biopsy (FNAB) material from 12 patients with histologically proven benign AMEs of the breast. RESULTS. All aspirates were moderately to highly cellular with large clusters composed of epithelium and myoepithelium. The myoepithelium was admixed with the ductal cells or was present as naked bipolar nuclei in 75% of samples. Small clusters or dispersed myoepithelial cells with epithelioid morphology were also present and showed intranuclear and intractyoplasmic vacuoles in one-third of samples. Mild-to-moderate nuclear atypia was noted in some samples, but no necrosis or mitoses were seen. None of the patients were diagnosed originally with AME: Two tumors were classified as benign and consistent with fibroadenoma, 6 tumors were atypical, 2 tumors were suspicious for carcinoma, and 2 tumors were positive for malignant cells. CONCLUSIONS. Because of the varied histology of AME, cytologic diagnosis of this neoplasm can be very challenging. Accurate identification of the myoepithelium is crucial to avoid misinterpretation as carcinoma. Conservative diagnosis and further histologic evaluation is recommended for these patients.