Anatomic Pathology: Soft Tissue Pathology

858) The microscopic image represents slowly growing 7 cm soft tissue mass in the thigh of a 65-year-old woman. Which one of the following is the MOST likely diagnosis?

• Hemangiopericytoma (HPC) /extrapleural solitary fibrous tumor is a slow-growing tumor of deep soft tissue, mainly localized to retroperitoneum and proximal extremities, with a small subset affecting the meninges.

• It mainly affects adults, with a peak in the fourth and fifth decades of life. HPC has a female predominance.

• HPCs are solid, circumscribed, stroma-poor lesions composed of uniform cells associated with delicate compressed to gaping, irregularly shaped vascular channels. The tumor cells are consistently CD34 positive. A wide immunohistochemical panel should be performed to exclude mimics, both benign and malignant.

• HPC of deep soft tissue is generally benign. Features that may be associated with malignancy are large size, cytologic atypia and tumor necrosis, and more than 4 mitoses per 10 HPF.

• Although a few cases have been associated with cytogenetic abnormalities, no consistent translocations are associated with HPC.

Enzinger FM, Smith BH: Hemangiopericytoma. An analysis of 106 cases. Hum Pathol 1976;7(1):61-82.

Espat NJ, Lewis JJ, Leung D, et al: Conventional hemangiopericytoma: modern analysis of outcome. Cancer 2002;95(8):1746-1751.

Sreekantaiah C, Bridge JA, Rao UN, et al:: Clonal chromosomal abnormalities in hemangiopericytoma. Cancer Genet Cytogenet 1991;54(2):173-181.

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