Cancer of the Small Intestine

The prevalence of cancer in the small intestine is low, with an incidence rate of 11 to 22 annual cases per one million people. Altogether, this entity occupies approximately three percent (Jemal 2008) of the working diagnoses in a general gastrointestinal (GI) oncology service (Bilimoria 2009). Yet, the incidence has been rising in an average rate of 2.3% each year in the past few years (Puccini et al. 2018). The low incidence is surprising, considering that the small intestine epithelium makes up more than 95% of the intestinal surface area. Moreover, unlike other GI cancers that include mostly adenocarcinoma, the histology of small intestine tumors is more diverse and comprises 45% adenocarcinoma, 30% neuroendocrine cancers, 15% lymphoma, and 10% sarcoma; those are mostly gastrointestinal stromal tumors (GIST). The prevalence of specific cancer types is influenced by location. While adenocarcinoma is the leading diagnosis in the duodenum, NET cancers are the leading diagnosis in the ileum. This chapter will focus mainly on adenocarcinoma of the small bowel while summarizing the current knowledge in the field and will provide directions for diagnosis and treatment.