Small Intestinal, Colorectal, and Appendicular Neuroendocrine Tumors

Intestinal neuroendocrine tumors (NETs) arise from the diffuse endocrine system present throughout its submucosal lining. These tumor cells are typically well-differentiated, slow growing, store various peptides and amino acids that, when secreted, can give rise to specific clinical syndromes. As tumor detection techniques, awareness, and education increase, the annual incidence has risen more than sixfold over four decades [1, 2]. With advancements in molecular biology, procedural techniques, medical therapeutics and imaging, clinical management has grown more complex with patients typically seen by multi-specialty teams focused on the unique characteristics of NETs. From the first recognition of the Kulchitsky cell being responsible for the synthesis, storage, and release of serotonin to the current state of theranostics and precision medicine, survival outcomes have improved. The epidemiology, biology, natural history, clinical presentation, and management of these intestinally derived well-differentiated malignancies are the focus of this review. Finally, the authors will address some current limitations, impact of the COVID-19 pandemic on NET patient care, and opportunities for the future.