Gastrointestinal neuroendocrine tumors (NETs): new diagnostic and therapeutic challenges.

This paper summarizes the current understanding of the biology of somatostatin receptor (sst), role of immunotherapy in neuroendocrine tumor (NET), new agents for PPRT, and methods to assess response and clinical benefit in NET. One of the most interesting aspects of sst biology is the recent discovery of truncated variants of the sst5 receptor subtype with unique tissue distribution and response to somatostatin (SST). These truncated receptors are associated with bad patient prognosis, decreased response to SST analogs, and may be new targets for diagnoses and treatment. IFN remains a cost-effective agent, particularly in classic mid gut carcinoids, and there is interest to continue examining immunotherapy's in this disease. PRRT remains a key strategy for treatment and imaging. In addition to the classic agents, there are a series of new agents targeting other receptors such as the incretin receptors (GLP-1R; GIPR) and other G-protein coupled receptors with great potential. With regards to therapy monitoring, the most commonly used criteria are Response Criteria Evaluation in Solid Tumors (RECIST). However, for different reasons, these criteria are not very useful in NET. Incorporation of other criteria such as Choi as well as functional imaging assessment with PET would be of great interest in this area.