[Hemangiopericytoma of the breast].

A rare case of hemangiopericytoma of the breast is reported with an electron microscopic study. The differential diagnosis is discussed. Ultrastructural study confirmed the diagnosis by revealing that the tumor cells were separated from the endothelial cells of the capillary and had abundant cytoplasmic filaments that formed dense plaques along the plasma membrane. The patient has remained free of tumor for four years after tumorectomy. A review of the literature on reported cases is also presented. Microscopically, benign and malignant forms could not be distinguished easily. It is necessary to followup behavior for more than five years if the tumor does not seem malignant.