Adenomyoepithelioma of the breast. A review of three cases with reappraisal of the fine needle aspiration biopsy findings.

OBJECTIVE: To describe the fine needle aspiration cytology findings of adenomyoepithelioma of the breast, with histologic correlation.

STUDY DESIGN: The author reviewed the cytologic findings of three cases of adenomyoepithelioma of the breast in the files of Pamela Youde Nethersole Eastern Hospital in a three-year period, 1998-2000. The diagnosis was confirmed by histologic examination, immunohistochemical study and electron microscopy.

RESULTS: All cases showed similar cytologic findings. The direct smears and cytospin preparations contained an obvious biphasic cell population. There were clusters and sheets of benign apocrine cells admixed with clumps of bland-looking oval to spindle cells. The apocrine cells contained larger, round nuclei; prominent solitary nucleoli; and ample eosinophilic, granular cytoplasm. In contrast, the spindle cells had oval nuclei, fine chromatin, inconspicuous nucleoli and scanty amphophilic cytoplasm. A small number of named nuclei and foamy macrophages was noted in the background. The characteristic stromal elements seen in fibroepithelial tumor of the breast were not found. The myoepithelial nature of the spindle cells was confirmed by immunohistochemical and ultrastructural studies. Subsequent simple mastectomy and wide local excision were performed on cases 1 and 2, respectively, revealing focal carcinomatous transformation in the adenomyoepitheliomas. The carcinoma cells, however, were not sampled in the initial cytologic specimens.

CONCLUSION: The cytologic features of adenomyoepithelioma, though variable and subtle, are characteristic enough for diagnosis. Recognition of the peculiar combination of benign apocrine cells and clumps of nondescript spindle cells should alert the cytologist to this rare but distinct entity, which carries a propensity for malignant transformation.