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Home > Treating NETs  > Disease Background > Understanding NETs

Understanding NETs

Neuroendocrine tumours (NETs) were first reported in 1907 by Siegfried Oberndorfer, who used the term “carcinoid” to name the benign, cancer-like neoplasms he observed in the small intestine.1

However, the classification of NETs has since been expanded to include additional tumour types and refined based on the location of the tumours, the types of hormones secreted, and the associated symptoms.

According to the WHO classification published in 2000, NETs can be classified histologically into 5 types2:

  • Well-differentiated neuroendocrine tumours (benign carcinoids)
  • Well-differentiated carcinomas (malignant carcinoids)
  • Poorly differentiated carcinomas (small cell carcinomas)
  • Mixed endocrine and exocrine carcinomas (such as adenocarcinoids)
  • Several extremely rare neuroendocrine-like lesions

The type of NET can be further distinguished by immunohistochemistry to identify specific bioactive substances produced by the cells. Several neuroendocrine markers are routinely tested for: chromogranin A (CgA), neuron-specific enolase (NSE), synaptophysin, serotonin, and gastrin. In addition, the proliferation capacity of the NETs is usually determined by staining with the mitotic markers Ki-67 or
MIB-1.2-4

Although the clinical symptoms of NETs are heterogenous, NETs can be broadly divided into 2 subgroups based on their clinical syndromes5:

  • Nonfunctioning tumours—when no specific clinical syndrome is observed
  • Functioning tumours—when the secreted products lead to clinical syndromes

In earlier stages of the disease, NET patients commonly have nonfunctioning tumours. These tumours may present with either no signs of the disease or
only vague symptoms, because metabolic products released by actively secreting NETs are rapidly destroyed by blood and liver enzymes. Thus, it is difficult to diagnose NETs at an early stage and diagnosis is typically delayed by
several years.6,7

Correct diagnosis is often made after NETs have developed into functioning tumours or have metastasised. These metastasised tumours release a
large concentration of peptide hormones and bioactive substances into the bloodstream, leading to the distinct clinical symptoms associated with
functioning NETs.1

References: 1. Modlin IM, Oberg K, Chung DC, et al. Gastroenteropancreatic neuroendocrine tumours. Lancet Oncol. 2008;9:61-72. 2. Warner RRP. Enteroendocrine tumors other than carcinoid: a review of clinically significant advances. Gastroenterology. 2005;128:1668-1684. 3. Oberg K, Jelic S; on behalf of the ESMO Guidelines Working Group. Neuroendocrine gastroenteropancreatic tumors: ESMO clinical recommendations for diagnosis, treatment and follow-up. Ann Oncol. 2008;19(suppl 2):ii104-ii105. 4. Oberg K. Neuroendocrine gastroenteropancreatic tumours—current views on diagnosis and treatment. Eur Oncol Rev. 2005:1-6. 5. Fazio N, de Braud F, Delle Fave GD, Oberg K.
Interferon-α and somatostatin analog in patients with gastroenteropancreatic neuroendocrine carcinoma: single agent or combination? Ann Oncol. 2006:1-7. 6. National Comprehensive Cancer Network. Neuroendocrine tumors. In: Practice Guidelines in Oncology—v.1. Fort Washington, PA: National Comprehensive Cancer Network; 2008. 7. Modlin IM, Moss SF, Chung DC, Jensen JT, Synderwine E. Priorities for improving the management of gastroenteropancreatic neuroendocrine tumors. J Natl Cancer Inst. 2008;100:1282-1289.