Hybrid schwannoma-perineurioma frequently harbors VGLL3 rearrangement

Benign peripheral nerve tumors include schwannoma, neurofibroma, and perineurioma, as well as a recently recognized group of tumors with dual patterns of differentiation. The molecular pathogenesis of these so-called "hybrid" tumors remains poorly understood. Following identification of a novel CHD7-VGLL3 fusion gene in a hybrid schwannoma-perineurioma, we evaluated an expanded cohort of this tumor-type-as well as tumors with VGLL3 rearrangement identified from a curated molecular database-to characterize the prevalence of fusion genes among these tumors. Eighteen tumors met the inclusion criteria for this study. RNA sequencing identified VGLL3 rearrangement in 14 of these cases; the partner genes included CHD7 (ten cases), CHD9 (two cases), and MAMLD1 (two cases). Two cases possessed altogether unrelated fusions, including: DST-BRAF and SQSTM1-CDX1 fusion genes. Finally, two cases lacked identifiable fusion products. These findings highlight the molecular diversity of these neoplasms, with frequent rearrangement of VGLL3. More importantly, despite their dual pattern of differentiation, our results reveal the pathogenesis of hybrid schwannoma-perineurioma is unrelated to conventional schwannoma and perineurioma, thereby implying this tumor represents an altogether pathologically distinct entity.