Less Common Types of Pancreatic Neuroendocrine Tumors

Neuroendocrine tumors (NET) are group of heterogeneous disorders with a wide range of biological and clinical behavior. They are most commonly located in the gastroenteropancreatic system and the lungs. Although NETs are considered to be rare, there are even more rare subtypes of NETs. For example, functional pNETs represent less than 10% of pNETs. Their clinical behavior is very heterogenous with a changing disease course such as malignant tumors showing a slow growth or malignant behavior in a previously benign lesion. They can also be associated with familial genetic syndromes leading by MEN1. In MEN1 syndrome, the reported frequency glucagonomas and VIPomas are around 3% and GRHomas, somatostatinomas are around 1%. Another well-known association is the presence of up to 10% somatostatinoma in neurofibromatosis type 1, and there is a 10% risk of pNET in von Hippel Lindau disease and the vast majority of these NETs cases are also non-functional. Tuberous sclerosis is another inherited disorder with around 20 reported cases of accompanying pNET with rare NET subtype. In this chapter, we will discuss the general clinical features, diagnosis, and treatments of rare functional pNETs and discuss some distinct clinical syndromes related with rare functional pNETs, such as GRHomas, ACTHoma, PTHroma, Ghrelinoma, calcitoninoma, and serotoninoma. The mainstay of treatment at earlier stage is surgery. The data on the medical treatment of these rare NETs are scarce and the recommendations are mostly based on the studies including all pNET patients. Somatostatin analogs are the mainstay of treatment as an effective option in the control of symptoms, especially in VIPomas, GRHomas, glucagonomas, and in some cases of somatostatinomas.