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Solitary Fibrous Tumor : Differential

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Differential Diagnosis of Solitary Fibrous Tumor:

Deep fibrous histiocytoma: It is composed of more uniform spindle cells with a storiform arrangement and may show focal hemangiopericytomatous pattern. Other features include lymphocytic infiltrate, foamy cells, hyaline change, and osseous metaplasia. About 40% of cases show CD34 positivity further increasing confusion with solitary fibrous tumor (SFT). However, STAT6 is negative (unlike SFT). Many of these lesions tend to involve the orbital soft tissues.

Synovial sarcoma: About 10-20% of synovial sarcomas have focal hemangiopericytoma-like areas. Features favoring synovial sarcoma include biphasic appearance (glands + spindle cells), expression of cytokeratin, negativity for CD34 and STAT6 and nuclear positivity for TLE1. In addition, synovial sarcoma carries the t(X;18)(p11.2;q11.2) translocation.

Other entities include GIST, de-differentiated liposarcoma, MPNST, mesenchymal chondrosarcoma, and low-grade fibromyxoid sarcoma.

The image shows a solitary fibrous tumor that had most of the morphologic features associated with malignancy (size >5 cm, hypercellularity, cytologic atypia, >4 mitoses/10 hpf, and necrosis.

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