Solitary Fibrous Tumor of the Vulva: Report of 2 Cases, Including a De Novo Dedifferentiated Solitary Fibrous Tumor Diagnosed After Molecular Demonstration of NAB2-STAT6 Gene Fusion.

Solitary fibrous tumor (SFT) is a neoplasm of fibroblastic lineage that has been documented in almost every anatomic location. Vulval SFT is very rare with only 10 cases reported to date. We present 2 additional SFTs located in the vulva, in adult women of 59 and 25 yr of age. The first showed a classic morphology and immunophenotype with uniform and strong STAT6 nuclear expression. The other one was a spindle-cell de novo dedifferentiated SFT with heterogeneous nuclear and cytoplasmic STAT6 staining, which could only be correctly diagnosed after molecular analysis with demonstration of a NAB2-STAT6 gene fusion. This genetic aberration is considered to represent the major pathogenic driver …