Fine-needle aspirates of granular cell lesions of the breast: report of three cases, with emphasis on differential diagnosis and utility of immunostaining for CD68 (KP1).

Fine-needle aspiration biopsy (FNA) has been recognized as a safe and reliable procedure for evaluating breast lesions. We herein report cytologic findings for needle aspirates from three granular cell nodules of the breast. The nodules were detected by diagnostic imaging and ranged from 0.6 to 1 cm in diameter. Ultrasound-guided FNA was used in all cases and revealed cellular aspirates with similar cytomorphologic features consisting of sheets of large granular cells intersected by arborizing thin-walled blood vessels. The cells had round to oval nuclei, inconspicuous nucleoli, and abundant, often ill-defined granular cytoplasm. Tissue sections of resected specimens yielded final diagnoses of granular cell metaplasia of histiocytes and stromal cells in one case and granular cell tumor (GCT) in the other two cases. FNA smears in all three cases were strongly positive for the lysosomal marker CD68 (KP1) and S-100 protein; therefore, it was not possible to distinguish true GCT from granular cell metaplasia/granular histiocytes. When breast aspirates reveal granular cell changes, excisional biopsy should be done for a definitive diagnosis.