Hemangiopericytoma of the breast.

Hemangiopericytoma is an extremely rare soft tissue tumor of the pericytes that surround the walls of blood vessels. The lesion is characterized by proliferation of the pericytes above the basement membrane. The microscopic features of the hemangiopericytoma can often be demonstrated by reticulin staining. Clinical presentation can vary. The lesion has been found in any number of anatomic locations. Occurrence in breast tissue, however, has been strikingly rare. Most lesions are benign. However, they can be aggressive and can recur at distant sites. Malignant varieties have been reported. In breast tissue, the most difficult aspect of the diagnosis appears to be that the tumor grossly, and to some extent microscopically, resembles cystosarcoma phylloides, particularly in the malignant degenerative form of the latter disease. Most diagnostic methods for evaluating the tumor fail to produce a definitive diagnosis. Microscopic confirmation is perhaps the only method by which definitive diagnosis can be made. Treatment consists of wide excision and careful clinical follow-up. A case history and a review of the literature concerning this lesion are included here.