Solitary fibrous tumor is a deep soft tissue tumor of uncertain histogenesis. The term solitary fibrous tumor now includes entity previous called hemangiopericytoma. This is based on histologic similarities between the two tumors, including staghorn vessels and positivity of CD34. Hemangiopericytoma is regarded as a cellular phase of solitary fibrous tumor. The photographs shows a solitary fibrous tumor that presented as a slow growing soft tissue mass in the thigh of an adult male. Image copyright: pathorama.ch.