摘要Background Pleomorphic hyalinizing angiectatic tumor (PHAT) of soft parts is a rare soft tissue tumor, which is generally considered low-grade. To distinguish the tumor from other soft tissue lesions, we analyzed the clinicopathologic and ultrastructural features, immunophenotypes, and flow cytometric DNA ploidy of PHAT in 9 cases.Methods PHAT specimens were collected from 9 patients with PHAT from 1990 to 2004. Each specimen was cut into pieces and stained with hematoxylin-eosin, phosphotungstic acid-hematoxylin, Prussian blue, and Masson trichrome,respectively. Immunohistochemical stains for vimentin, S-100 protein, CD34, CD31, CD99, VEGF, desmin, CD117, α-SMA,and MIB-1 were performed with the Envision system. Flow cytometry was used in four specimens, two of which were observed by electron microscopy.Results In the 9 cases, the PHAT occurred at the lower extremity in 2 patients, inguinal in 2, waist in 1, forearm in 1,buttock in 1, foot in 1, and the chest wall in 1. All the lesions presented in the superficial subcutaneous tissues. Follow-up data were available in 7 of the patients, among whom 2 (28.6%) had recurrence after primary therapy. Microscopically,typical PHAT was characterized by sheet-like proliferation of spindle or pleomorphic cells and clusters of thin-walled hyalinized cstatic vessels. In some areas of the tumor, hemosiderin-laden spindle cells, numerous small single vessels,and myxoid extracellular matrix could be identified, indicating an "atypical PHAT". Mitotic figures were rare in all the cases.In 5 of the 9 patients (55.6%), the tumor was typical PHAT; and in the other 4 (44.4%), typical and atypical PHAT coexisted. Immunohistochemically, the neoplastic cells were positive for vimentin, CD34, CD99, and VEGF, but negative for S-100 protein, desmin, SMA, and CD31. In all the cases, the MIB-1 proliferative activity of the neoplastic cells was lower than 2%. Ultrastructural analysis did not reveal any evidence of specific differentiation. Aneuploidy was not detected by flow cytometry.Conclusions Histologically, typical PHAT is characterized by spindle and pleomorphic cells associated with an angiectatic vasculature. The neoplastic cells often express vimentin and CD34, and may be positive for CD99 and VEGF.Ultrastructurally, the tumor usually has no specific differentiation. The low MIB-1 index and the absence of aneuploidy in PHAT indicate a non-malignancy. However, we consider the tumor as a borderline neoplasm because of its aggressive behaviour, and suggest wide local resection with tumor-free margin for the treatment of the disease.