Aneurysmal bone cyst (ABC) is a locally recurrent bone lesion that has been regarded as a reactive process. Recently, a neoplastic basis in primary ABC was evidenced by demonstration of clonal chromosome band 17p13 translocations that place the USP6 (TRE2 or TRE17) oncogene under the regulatory influence of the highly active CDH11 promoter. Herein, we report CDH11 and/or USP6 rearrangements in 36 of 52 primary ABCs (69%), of which 10 had CDH11-USP6 fusion, 23 had variant USP6 rearrangements without CDH11 rearrangement, and three had variant CDH11 rearrangements without USP6 rearrangement. USP6 and CDH11 rearrangements were restricted to spindle cells in the ABC and were not found in multinucleated giant cells, inflammatory cells, endothelial cells, or osteoblasts. CDH11 and USP6 rearrangements did not correlate with recurrence-free survival, or with other clinicopathological features. CDH11 and USP6 rearrangements were not found in any of 17 secondary ABC associated with giant cell tumor, chondroblastoma, osteoblastoma, and fibrous dysplasia. These findings demonstrate that primary ABC are mesenchymal neoplasms exhibiting USP6 and/or CDH11 oncogenic rearrangements. By contrast, secondary ABC lack CDH11 and USP6 rearrangements, and although morphological mimics of primary ABC, appear to represent a non-specific morphological pattern of a diverse group of non-ABC neoplasms.

The development of MSOs with PTC features is associated with BRAF mutations of the type commonly observed in PTC, suggesting a common pathogenesis for all PTCs regardless of location. In contrast, mutations in the RET/RAS/RAF pathway are not found in BSO. The prognostic significance of BRAF mutation status in MSO remains to be determined.

Chronic administration of drisapersen, a 2 0 -OMe phosphorothioate antisense oligonucleotide (AON) to mice and monkeys resulted in renal tubular accumulation, with secondary tubular degeneration. Glomerulopathy occurred in both species with species-specific characteristics. Glomerular lesions in mice were characterized by progressive hyaline matrix accumulation, accompanied by the presence of renal amyloid and with subsequent papillary necrosis. Early changes involved glomerular endothelial hypertrophy and degeneration, but the chronic glomerular amyloid and hyaline alterations in mice appeared to be species specific. An immune-mediated mechanism for the glomerular lesions in mice was supported by early inflammatory changes including increased expression of inflammatory cytokines and other immunomodulatory genes within the renal cortex, increased stimulation of CD68 protein, and systemic elevation of monocyte chemotactic protein 1. In contrast, kidneys from monkeys given drisapersen chronically showed less severe glomerular changes characterized by increased mesangial and inflammatory cells, endothelial cell hypertrophy, and subepithelial and membranous electron-dense deposits, with ultrastructural and immunohistochemical characteristics of complement and complement-related fragments. Lesions in monkeys resembled typical features of C3 glomerulopathy, a condition described in man and experimental animals to be linked to dysregulation of the alternative complement pathway. Thus, inflammatory/immune mechanisms appear critical to glomerular injury with species-specific sensitivities for mouse and monkey. The lower observed proinflammatory activity in humans as compared to mice and monkeys may reflect a lower risk of glomerular injury in patients receiving AON therapy.