Non-central nervous system
hemangiopericytoma (HPC) and
solitary fibrous tumor (SFT) are considered by pathologists as two variants of a single
tumor entity now subsumed under the entity SFT. Recent detection of frequent NAB2-STAT6 fusions in both, HPC and SFT, provided additional support for this view. On the other hand, current neuropathological practice still distinguishes between HPC and SFT. The present study set out to identify genes involved in the formation of meningeal HPC. We performed exome sequencing and detected the NAB2-STAT6 fusion in
DNA of 8/10 meningeal HPC thereby providing evidence of close relationship of these
tumors with peripheral SFT. Due to the considerable effort required for exome sequencing, we sought to explore
surrogate markers for the NAB2-STAT6 fusion
protein. We adopted the Duolink proximity
ligation assay and demonstrated the presence of NAB2-STAT6 fusion
protein in 17/17 HPC and the absence in 15/15
meningiomas. More practical, presence of the NAB2-STAT6 fusion
protein resulted in a strong nuclear signal in STAT6 immunohistochemistry. The nuclear reallocation of STAT6 was detected in 35/37 meningeal HPC and 25/25 meningeal SFT but not in 87
meningiomas representing the most important differential diagnosis. Tissues not harboring the NAB2-STAT6 fusion
protein presented with nuclear expression of NAB2 and cytoplasmic expression of STAT6
proteins. In conclusion, we provide strong evidence for meningeal HPC and SFT to constitute variants of a single entity which is defined by NAB2-STAT6 fusion. In addition, we demonstrate that this fusion can be rapidly detected by STAT6 immunohistochemistry which shows a consistent nuclear reallocation. This immunohistochemical assay may prove valuable for the differentiation of HPC and SFT from other mesenchymal
neoplasms.