Solitary fibrous tumor

Definition

A rare soft tissue tumor characterized by a well-circumscribed mass potentially occurring at any anatomical site, histopathologically showing spindled to ovoid cells arranged around a branching and hyalinized vasculature and variable stromal collagen deposition. Immunohistochemistry reveals CD34 and/or STAT6 expression. NAB2-STAT6 gene fusions are pathognomonic for this tumor, which may be malignant or benign. Clinically, most patients present with a slow-growing, painless mass. Large tumors may cause paraneoplastic syndromes such as Doege-Potter syndrome, with the induction of severe hypoglycemia or acromegaloid features.