Myxoid solitary fibrous tumor: a study of three cases.

Limited myxoid areas are usually encountered in solitary fibrous tumor (SFT), but SFT with abundant myxoid stroma has only been reported occasionally. Myxoid SFT is defined as having myxoid changes in 50% or more of the tumor. We review the literature on myxoid SFT and add 3 new cases to those previously described. Microscopically, the lesions were composed of spindle cells arranged in a haphazard or storiform pattern in a cellular and hypocellular myxoid background with thin-walled "staghorn" branching vessels. Atypical features (necrosis, hypercellularity, or increased mitotic figures) were not identified. All cases were positive for CD34 and CD99 and had a benign course with a follow-up ranging from 15 to 70 months. Our review suggests that like classical SFT, myxoid SFT is associated with an indolent clinical course and favorable prognosis. Their recognition is crucial to distinguish a variety of myxoid spindle cell neoplasms with different prognoses and treatment options.