Fibroepithelial tumor of the breast with digital fibroma-like inclusions in the stromal component. Case report with immunocytochemical and ultrastructural analysis.

A case of fibroepithelial tumor of the breast in a 34-year-old woman, showing digital fibroma-like inclusions in the stromal component is presented. Morphological, immunocytochemical, and ultrastructural findings indicate that the peculiar eosinophilic intracytoplasmic inclusions observed may represent tightly packed actin filaments. Although they are more frequently detected within digital fibrous proliferations of infancy, their rare occurrence at either unusual site or in adulthood has been reported. Similar inclusions have also been rarely observed in intranodal myofibroblastoma and in benign leiomyomas. These findings suggest that these inclusions may be the result of some metabolic or organisational abnormality shared by neoplastic actin-rich cells. Myofibroblastic and smooth muscle lesions are probably the commonest to show this defect.