Spindle Cell Neoplasms Unique to the Sinonasal Tract.

The spindle cell neoplasms include sinonasal tract angiofibroma (STA), glomangiopericytoma (GPC), and biphenotypic sinonasal sarcoma (BSNS). These entities share some clinical, histomorphologic, immunohistochemical, and even molecular characteristics. Nevertheless, there are features that are unique to each tumor type. STA shows heavily collagenized and vascular stroma, with apparent relationship to underlying hormonal changes. GPC consistently exhibits monomorphic, ovoid cytologic appearance with the constant feature of Beta-catenin nuclear accumulation by IHC. Lastly, BSNS is a deceptively bland and neural-like neoplasm featuring consistent co-expression of S100 and smooth muscle markers with specific genetic rearrangements serving to uniquely characterize this entity.