Fine needle aspiration cytology of adenosis tumor of the breast. With immunocytochemical and ultrastructural observations.

The fine needle aspiration (FNA) findings of multinodular sclerosing adenosis forming a discrete lesion (so-called "adenosis tumor") of the breast are presented. The findings in this case and a review of the literature indicate that adenosis tumor is an unusual breast lesion that can clinically and histologically be confused with breast carcinoma, especially at the time of frozen section. FNA biopsy demonstrated uniform groups of ductal cells, stromal fragments and many stripped bipolar nuclei, which led to a correct diagnosis of a benign proliferative breast lesion, but not to a specific diagnosis of adenosis tumor. Immunoperoxidase staining for muscle actin demonstrated positive staining of many bipolar spindle-shaped cells, indicative of myoepithelial cells. Immunohistochemical studies on the resected specimen demonstrated actin positivity of myoepithelial cells and intact linear staining of type IV collagen around the ductules. Ultrastructural examination demonstrated ductal cells with surrounding myoepithelial cells resting on a delicate basal lamina, with surrounding bundles of collagen in the interstitial space. This appears to be the first FNA cytologic description of this unusual breast tumor and the first immunohistochemical and ultrastructural characterization of this lesion. FNA cytologic examination may more clearly identify the benign nature of the breast mass than frozen section.