Hemangiopericytoma of the breast.

The clinical and pathologic features of three hemangiopericytomas of the breast in women are described. The three tumors presented as painless, nontender nodules. The morphologic variation typical of hemangiopericytomas was present in each tumor. One case was studied by electron microscopy and was found to be composed of two types of pericytes. Both cell types were closely associated with vessels, partially or completely surrounded by basal lamina, and contained pinocytotic vesicles. There were only minor differences between the two forms of pericytes. Smooth muscle cells, fibroblasts, or transitional cell forms were not observed. The two patients on whom follow-up information was available have remained free of tumor 2.8 and 4 years after their surgery, indicating that not all vascular tumors of the breast are highly aggressive neoplasms.