Perez-Rivas LG, et al. - This study was performed to examine whether somatic ubiquitin-specific protease 8 (USP8) mutations were frequent events in corticotroph tumor progression causing Nelson's tumor. In Nelson's tumors, somatic mutations in USP8 were common, showing that they did not drive the corticotroph tumor progression that led to Nelson's syndrome. They could be correlated with a less favorable biochemical outcome after surgery for Nelson's tumor.