Collagenous spherulosis. Report of a case with diagnosis by fine needle aspiration biopsy with immunocytochemical and ultrastructural observations.

Collagenous spherulosis (CS) is a benign breast lesion usually seen in association with other benign proliferative processes in the breast. To the best of our knowledge, this is the second fine needle aspiration (FNA) cytologic report of CS and the first with corresponding immunocytochemical and ultrastructural studies performed on the subsequent biopsy material. Cytologically, the aspirate consisted of scattered, metachromatically staining hyaline globules seen best with Diff-Quik stain in intimate association with numerous groups of benign ductal cells some of which had a papillary configuration. The globules exhibited periodic acid-Schiff positivity. A subsequent excisional biopsy confirmed the cytologic impression and revealed a multifocal process of ductal papillomas and papillomatosis containing numerous eosinophilic spherules with morphologic features and histochemical staining reactions typical of CS. Electron microscopic and immunoperoxidase studies suggest the spherules to be composed predominantly of basement membrane proteins, specifically type IV collagen, laminin and fibronectin, and to be derived principally from myoepithelial cells. Although CS has been found primarily in benign breast lesions, it can be found in other organs and in association with both benign and malignant processes. The differential diagnosis of other breast lesions that can be confused with CS on FNA biopsy is presented.