Neuroendocrine tumors (NETs) belong to the family of solid malignant neoplasms that are believed to originate from neuroendocrine cells found throughout the body.1 There are several types of NETs, each warranting a different clinical approach in terms of diagnosis and management. Many of these neoplasms traditionally have been called "carcinoids," but this term does not accurately account for their variable biology, histologic differentiation, and secretory potential.2,3
A Word About NET Nomenclature
Because of this heterogeneity, different naming conventions for NETs have been used for years. This Web site uses the nomenclature established in the 2010 WHO Classification of Tumours of the Digestive System to classify different types of neuroendocrine neoplasms.4
The WHO classification guidelines categorize these neoplasms into 2 groups4:
- Neuroendocrine tumors (NETs): well-differentiated neoplasms that can be divided into grade 1 (G1) and
grade 2 (G2) depending on proliferation and histology - Neuroendocrine carcinomas: poorly differentiated grade 3 (G3) neuroendocrine neoplasms
WHO 2010 Classification of Neuroendocrine Neoplasms4,5
WHO and other classification guidelines also emphasize the importance of proliferative index in classifying NETs because of the markedly different metastatic potential they exhibit.6 NETs may also be classified by site of origin, which includes the GI tract, the lungs and thymus, and the pancreas.
Neuroendocrine tumors (NETs):
Anatomic distribution
Common features, diverse presentation
Depending on the type of NET, it may produce nonspecific symptoms that are easily mistaken for those of other conditions, or it may remain clinically silent for years.9 Vague symptoms may include flushing, fatigue, diarrhea, hypoglycemia, skin changes, abdominal pain/discomfort, and wheezing.1,9,10 Some symptoms or syndromes associated with NETs may be influenced by genetic factors, such as MEN-1, as well as MEN-2a and MEN-2b.9
Despite diverse tissues of origin, NETs share many common features, including:
- Pathologically definable growth patterns
- Potential to secrete bioactive products (most commonly serotonin or peptides, such as insulin, gastrin, and glucagons)
- Expression of neuroendocrine markers including chromogranin A (CgA)
NETs, including small neoplasms (<2 cm), have the potential to metastasize.11-13 According to a 30-year analysis of the Surveillance Epidemiology, and End Results (SEER) database, 50% of all patients with reported disease stage have either regional or distant metastases at diagnosis.14
A closer look at NETs
Download frequently asked questions about NETs.
