Neuroendocrine neoplasms can be characterized by their1,4,10
Many characteristics of NETs are site specific,11 and most NETs arise in these locations4,8:
Despite these varied tissues of origin, all NETs
It is important to note primary tumors are often small,3,12 which may contribute to diagnosis being delayed until after the tumor has metastasized.4,13
The WHO 2010 guidelines divide neuroendocrine neoplasms into 2 clinically distinct pathologic classes: well- and poorly differentiated.
Some of the biological behavior exhibited by neuroendocrine neoplasms is highly correlated with neoplasm grade10,16:
The Surveillance, Epidemiology, and End Results (SEER) program database uses a "localized," "regional," and "distant" system to stage disease. NETs are also staged using this system.16
The SEER database is a comprehensive cancer statistics program operated by the National Cancer Institute. SEER is widely used to establish the epidemiologic landscape for various types of cancer throughout the world.
Additionally, the Worldwide Health Organization (WHO), the Union for International Cancer Control (UICC), and the American Joint Committee on Cancer (AJCC) classification systems reflect the widespread recognition that NETs should be staged using tumor-node-metastasis (TNM) staging criteria. In TNM guidelines, the fundamental staging landmarks for NETs parallel those used for carcinomas of the corresponding organs.1,16
Finally, NETs can be classified by whether or not they are capable of producing hormonal substances. This is sometimes referred to as functional status.7,13,19
Most NETs are nonfunctional, and some NETs remain asymptomatic indefinitely. Many of the symptoms and syndromes that NETs can cause do not occur until the tumor has metastasized.3,12 In fact, about 50% of patients with reported disease stage have either regional or distant metastases at diagnosis.4