NAB2-STAT6 Gene Fusion in Solitary Fibrous Tumor
Molecular Pathology of Solitary Fibrous Tumor (SFT) : Several balanced translocations, including t(12;19), t(13;22), and t(3;12) have been found in SFT. The most frequent cytogenetic alteration is rearrangements of 12q. More recently, solitary fibrous tumors (both benign and malignant) have been found to have an intrachromosomal inversion, inv12(q13q13), which juxtaposes NAB2 gene and STAT6 gene on 12q13. NAB2 and STAT6 are adjacent genes which are normally transcribed in opposite directions. NAB2 is a repressor of early growth response (EGR) zinc-finger transcription factors that regulate cell proliferation and differentiation. The juxtaposition of STAT6 converts NAB2 from a repressor to an activator of EGR causing tumorigenesis. The NAB2-STAT6 fusion protein drives nuclear expression of STAT6 which has been exploited immunohistochemically. Immunostaining with STAT6 antibody (nuclear expression; see next image)) has become extremely useful in diagnosing CD34-negative SFT as well as in distinguishing SFT from its histologic mimics with staghorn vasculature and/or CD34 immunoreactivity.