Neuroendocrine neoplasms of the appendix

Definition

• WHO groups
  • Well differentiated (Grade 1 - 3 NETS)
  • Poorly differentiated neuroendocrine carcinomas (small and large cells type)
  • Mixed neuroendocrine-non-neuroendocrine neoplasms
    • Treated as high grade NECs

Incidence

• 1 in every 150-300 appendectomies

Carcinoid syndrome

• Given the appendix is a midgut structure - is more likely than foregut or hindgut NETs to result in carcinoid syndrome
• Is less likely than small bowel NETS to cause carcinoid syndrome

Staging

• NB: Goblet cell adenocarcinomas and high-grade neuroendocrine carcinomas are staged as per appendiceal carcinomas.

Investigations

Indications for staging workup

• Tumours > 2cm
• Incomplete resection - lack of nodes or a positive margin.
• Concern for distant metastasis based on clinical symptoms.
• Staging modalities
  • CT or MRI to evaluate the liver
  • PET CT Dotatate to look for other metastatic disease.
• Blood tests
  • Chrοmοgrаոiո A (CgΑ) and measurement of the serotonin metabolite 5-hydroxyindoleacetic acid (5-ΗIAA) in a 24-hour urine collection
    • Not routinely done - if concern for distant disease/carcinoid syndrome

Colonoscopy

• 20% of NETs are associated with a synchronous non-NET neoplasm - of which 25% are colorectal cancers.

Prognosis

• Tumours <2cm are highly unlikely to have metastasized.
• 1/3 of tumours > 2cm are metastatic at diagnosis - usually to lymph nodes.
• Perforation of appendicitis does no appear to influence prognosis of classical appendiceal NETS.

Treatment

• The majority of patients will be diagnosed and treated after a appendicectomy.

Indications for a right hemicolectomy

• Tumours > 2cm.
• Tumours between 1-2cm with deep mesoappendiceal invasion (>3mm)
• Positive or unclear margins.
• Grade 2+
• LVI
• Mixed histology (i.e. goblet adenocarcinoma)