**1. Introduction**

Gastrointestinal neuroendocrine tumors make up a group of heterogeneous neoplasms of somewhat unpredictable biological and clinical behavior. These tumors arise mainly in the digestive tract but can occur in other organs that harbor neuroendocrine cells. They are considered complex tumors and of unpredictable clinical evolution due to the variety of attributes that they possess as the potential capacity of secretion of a large variety of peptides.

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Although they may appear benign tumors for a certain period of time, they can originate tissue infiltration and give metastasis. All these pathophysiological attributes of neuroendocrine tumors, which may occur in varying degrees of intensity in different patients, arouse general interest, and so they are studied by professionals from different expertise. In this chapter, we will turn to the study of some relevant aspects of these tumors that originate in the stomach. However, since these neoplasias are part of a large family of gastrointestinal tumors, we will carry out a summary review of the main attributes of this family which should be useful to better understand some nuances of these tumors which originate in the stomach.
