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5 things you should know about the surgical treatment of gastrointestinal neuroendocrine tumors
Posted in Lectures on 22 October 2019

Roser Termes Serra 
General Surgery Resident
Hospital Clinic (Barcelona, Spain)

Small intestinal neuroendocrine tumors:

Small intestinal NETs can occur anywhere from the duodenum to the terminal ileum, but they are most frequently found in the ileum within 60 cm from the ileocecal valve. They can be solitary tumors or multifocal (in 25% of affected patients). These tumors tend to produce both regional and distant metastases (37% and 27% respectively, on presentation), irrespective of size, even if they measure less than 1 cm. 

The treatment for patients with nonmetastatic tumors consists in resecting the involved segment and its mesentery. The remainder of the small intestine should always be examined properly at the time of surgery, because of the high probability of multifocal tumors.  

In patients with known metastatic tumors, resection of the primary tumor may be advised in order to reduce the potential of intestinal obstruction or bleeding, and abdominal pain. Nevertheless, this remains a controversial area. 

 

Colorrectal neuroendocrine tumors (nonappendiceal):

Colonic and rectal NETs are slightly different. Colonic tumors are larger and more aggressive, with at least 40% metastatic tumors on diagnosis. They are most frequently right sided and are usually asymptomatic until they are locally advanced. By contrast, rectal NETs tend to be smaller and are usually localized on presentation.

The treatment for colonic NETs is similar to that for colonic adenocarcinomas. A formal partial colectomy and regional lymphadenectomy is recommended, except for small incidentally detected tumors completely removed with an endoscopic polypectomy. In this case, endoscopic surveillance alone can be considered. 

In the case of rectal tumors, the treatment is similar. If the tumor is smaller than 1 cm and confined to the mucosa or submucosa (and most of them are), an endoscopic resection with negative margins is usually enough. However, tumors larger than 2 cm and those that invade the muscularis propria should be treated with radical surgical resection (low anterior resection or abdominoperineal resection). The treatment for intermediate-sized tumors is controversial. It is generally accepted that tumors without risk factors (elevated mitotic rate, lymphovascular invasion, etc.) can be treated with endoscopic resection, and tumors that show any risk factor should be treated with radical surgery. 

 

Appendiceal neuroendocrine tumors:

Appendiceal NETs are usually asymptomatic and often detected during an appendicectomy. Their prognosis is best estimated by tumor size. Almost 95% of them are smaller than 2 cm and they have a low probability of having metastases on diagnosis. 

 

Appendiceal NETs can be considered cured with only an appendicectomy if they

  • Are smaller than 1 cm
  • Are confined to the tip of the appendix
  • Do not invade the mesoappendix and have no evidence of lymphovascular invasion
  • Are well differentiated 

 

By contrast, a formal right hemicolectomy is advised if the tumor

  • Is larger than 2 cm 
  • Invades the mesoappendix or the appendiceal base
  • Shows lymphovascular invasion
  • Has an intermediate- or high-grade histology.

 

The treatment for tumors between 1 and 2 cm in size is also controversial, and there is no clear evidence about whether or not a right hemicolectomy should be performed.