Fine-needle aspiration cytologic study of myofibroblastoma of the breast. Immunohistochemical and ultrastructural findings.

Myofibroblastoma of the breast is a recently recognized benign stromal tumor arising from the breast mesenchyma. Myofibroblastomas are grossly circumscribed, unencapsulated tumors that are most commonly found in males. Histologically, myofibroblastomas comprise predominantly bipolar spindle cells arranged either haphazardly or in fascicles that traverse a collagenous background. Their ultrastructural and immunohistochemical profiles are consistent with myofibroblastic differentiation. Myofibroblastoma of the breast was discovered in a 64-year-old man. For the first time the fine-needle aspiration findings are reported, as are the histologic, immunohistochemical, and ultrastructural findings.