Diabetes secondary to neuroendocrine gastroenteropancreatic tumors

Neuroendocrine tumors (NET) of the gastroenteropancreatic (GEP) tract are heterogeneous neoplasms originating from multipotent stem cells in the gastrointestinal tract and pancreas. The incidence of NET has shown a marked increase over the last decades, and nowadays GEP NET represent the second most common gastrointestinal neoplasm after colorectal adenocarcinoma. They can be associated with a broad range of local and systemic symptoms, related to both tumor mass effects and/or secretion of several hormones and biogenic amines, this latter being a peculiar characteristic of this kind of neoplasm. As a number of other endocrine disorders, GEP NET can be associated with varying degrees of imbalance of glucose metabolism up to diabetes mellitus. This may result from different causes, ranging from a direct tumor mass effect on the pancreas, total or partial pancreatectomy and hormone hyperproduction to an altered counterbalance of glycoactive hormone secretion due to medical therapy (such as somatostatin analog treatment). In this chapter, we provide an overview of the most common conditions causing GEP NET patients to develop glucose metabolism imbalance and we also describe the possible role of the current NET therapies in this context. Finally, practical clinical suggestions regarding the management of diabetes secondary to GEP NET are provided as well.