GCG and pancreatic neuroendocrine tumor: In addition, ARX expression has been associated with alternative lengthening of telomeres (ALT) and poor prognosis in pancreatic NETs, and while it is mainly expressed in glucagon-producing tumors in that location, it has also been expressed in a subset of insulin-producing pancreatic NETs with poor outcome (31–35); this finding emphasizes the importance of classification of NETs by transcription factor expression that may have prognostic value.