A case of mucinous spherulosis of the breast diagnosed retrospectively in FNA material.

We describe for the first time the cytologic features of mucinous spherulosis (MS), a variant of collagenous spherulosis (CS) of the breast characterized by cribiform structures containing lightly basophilic material, embedded in a loosely mucinous acellular background. Histologically, the lesion was part of a complex hyperplasia containing foci of sclerosing adenosis, and foci of atypical ductal hyperplasia (ADH). Immunohistochemical study showed reactivity with smooth muscle actin and focally for cytokeratin 14. Cytologic features of MS were recognized retrospectively and consisted of intermediate to large round hyaline spherules, naked or surrounded by myoepithelial cells. A fibrillary radial appearance was observed with Diff-Quick stain. We draw attention to the importance of recognizing these features because they can easily pose problems either by being overlooked or overdiagnosed as mucinous carcinoma. Differential diagnosis is briefly discussed.