Granular-cell tumor of the breast. A cytologic, immunohistochemical and ultrastructural study of two cases.

: Two primary granular-cell tumors of the breast are reported. Cytologically and histologically, these tumors had the classic features of small, eccentrically located nuclei and numerous periodic acid-Schiff-positive cytoplasmic granules. The characteristic cytologic features were best appreciated in touch imprints, not in frozen sections. Immunohistochemically, the tumors demonstrated diffuse cytoplasmic staining for S-100 protein but negative staining for myoglobin. The significance of these immunohistochemical staining characteristics, particularly in evaluating the possible histogenesis of these tumors, is discussed. The ultrastructural features of these two tumors are also presented and compared to findings reported by other investigators.