Fine needle aspiration (FNA) cytology of adenoid cystic carcinoma and adenomyoepithelioma of breast: two lesions rich in myoepithelial cells.

Adenoid cystic carcinoma and adenomyoepithelioma are relatively rare, but well described, breast lesions. The FNA cytology features in two cases of mammary adenoid cystic carcinoma and two cases of adenomyoepithelioma are described. In both cases of adenoid cystic carcinoma, aspirates consisted of tightly cohesive clusters of cells arranged around spheres and interconnecting cylinders of acellular material. The two aspirates of adenomyoepithelioma were composed of large tightly cohesive clusters of cells associated with small amounts of stromal material. In all four aspirates a dual population of epithelial and myoepithelial cells could be identified within cellular aggregates, and numerous bare nuclei were present. Histology revealed the characteristic features of adenoid cystic carcinoma and adenomyoepithelioma. Immunohistochemical staining of histological sections for S-100 protein and alpha-smooth muscle actin confirmed the presence of large numbers of myoepithelial cells within all four lesions, providing indirect evidence that bare nuclei in breast aspirates represent myoepithelial cells. The presence of a dual population of epithelial and myoepithelial cells and of numerous bare nuclei within a breast aspirate is generally indicative of a benign lesion. This is not always the case, as adenoid cystic carcinoma is a malignant tumour, and adenomyoepithelioma, while generally exhibiting benign behaviour, is capable of local recurrence and distant metastasis.