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'''Neuroendocrine tumors''', or more properly '''gastro-entero-pancreatic''' or '''gastroenteropancreatic neuroendocrine [[tumors]]''' ('''GEP-NETs'''), are cancers of the interface between the endocrine (hormonal) system and the nervous system.
'''Neuroendocrine tumors''', or more properly '''gastro-entero-pancreatic''' or '''gastroenteropancreatic neuroendocrine [[tumors]]''' ('''GEP-NETs'''), are cancers of the interface between the endocrine (hormonal) system and the nervous system.


==Historical Perspective==
Siegfried Oberndorfer, in 1907, was the first person to distinguish clearly what we now call GEP-NETs from other forms of cancer. He gave the term "carcinoid" to these tumors, because they were so slow-growing that he considered them to be "cancer-like" rather than truly cancerous.
In 1929, he reported that some such tumors were not so indolent – these he distinguished as what we now call PETs from what most authorities call carcinoids.
Despite the differences between the two categories, some doctors, including oncologists, persist in calling all GEP-NETs "carcinoid", even into the twenty-first century.
<ref>
"The term 'carcinoid' was introduced by S[iegfried] Oberndorfer in 1907 to distinguish carcinoids as less rapidly growing and well-differentiated epithelial tumors of the small intestine from the more aggressively growing adenocarcinoma of the gut.... Strictly speaking&nbsp;... the term 'carcinoid' [is] reserved for endocrine tumors of the gastrointestinal tract&nbsp;... and not for those of the pancreas.... The vagueness of the term 'carcinoid' results from its histological features which are almost identical with those of endocrine pancreatic tumors" (Arnold ''et al.'' 2004, 195).
<p>
"During his tenure at the Pathological Institute of the University of Munich, Oberndorfer noted in 1907 that the lesions were distinct clinical entities and named them 'karzinoide' ('carcinoma-like'), emphasizing in particular their benign features. In 1929 he amended his classification to include the possibility that these small bowel tumors could be malignant and also metastasize" (Modlin 2004).
<p>
Regarding the persistence of the term ''carcinoid'': on a PET news forum, a patient says "for over 4 yrs I was referred to as carcinoid. In fact even when it was discovered I was actually islet cell and the pathologist was questioned by my doctor (specialist in NET) about this the pathology said we classify all islet cell as carcinoid. Since then no matter how many times I say islet cell to a local doctor - oncologist, gastroendocrineologist, radiologist - you get the idea - they ALL continue to refer to me as carcinoid" (NET_IsletCell 2006).
</ref>


The earliest synthetic form of somatostatin used in the treatment of Neuroendocrine tumors was [[octreotide]], first marketed, by [[Sandoz]] as Sandostatin, in 1988.


==Classification==
===Human GEP-NETs by Site of Origin and by Symptom===
* Carcinoids (about two thirds of GEP-NETs)
** With carcinoid syndrome (about 10 percent of carcinoids)
** Without carcinoid syndrome (about 90 percent of carcinoids)
* PETs (about one third of GEP-NETs)
** Nonfunctioning (15 to 30 percent of PETs)
** Functioning (70 to 85 percent of PETs)
*** [[Gastrinoma]], producing excessive [[gastrin]] and causing [[Zollinger-Ellison Syndrome]] (ZES)
*** [[Insulinoma]], producing excessive [[insulin]]
*** [[Glucagonoma]], producing excessive [[glucagon]]
*** [[Vasoactive intestinal peptideoma]] ([[VIPoma]]), producing excessive [[vasoactive intestinal peptide]] (VIP)
*** [[PPoma]], producing excessive [[pancreatic polypeptide]] (often classed with nonfunctioning PETs)
*** [[Somatostatinoma]], producing excessive [[somatostatin]]
*** [[Watery diarrhea]], [[hypokalemia]]-[[achlorhydria]] (WDHA)
*** [[CRHoma]], producing excessive [[CRH|corticotropin-releasing hormonse]] (CRH)
*** [[Calcitoninoma]], producing excessive [[calcitonin]]
*** [[GHRHoma]], producing excessive [[GHRH|growth-hormone-releasing hormone]] (GHRH)
*** [[Neurotensinoma]], producing excessive [[neurotensin]]
*** [[ACTHoma]], producing excessive [[adrenocorticotropic hormone]] (ACTH)
*** [[GRFoma]], producing excessive [[growth hormone]] release factor (GRF)
*** [[Parathyroid hormone–related peptide tumor]]
* Rare GEP-NETs
** Medullary carcinoma of the [[thyroid]]
** [[Merkel cell cancer]] (trabecular cancer)
** [[Small-cell lung cancer]] (SCLC)
** Large-cell neuroendocrine carcinoma (of the lung)
** Neuroendocrine carcinoma of the [[cervix]]
** Multiple Endocrine Neoplasia type 1 (MEN-1 or MEN1) (usually nonfunctioning) (also causing ZES)
** Multiple Endocrine Neoplasia type 2 (MEN-2 or MEN2)
** [[Neurofibromatosis type 1]]
** [[Tuberous sclerosis]]
** [[Von Hippel-Lindau disease]]  (VHL)
** [[Neuroblastoma]]
** [[Pheochromocytoma]] (phaeochromocytoma)
** [[Paraganglioma]]
** Neuroendocrine tumor of the anterior [[pituitary]]
** Carney's complex
===Classification of GEP-NETs by cell characteristics===
The diverse and amorphous nature of GEP-NETs has led to a confused, overlapping, and changing terminology. In general, aggressiveness (malignancy), secretion (of hormones), and anaplasia (dissimilarity between tumor cells and normal cells) tend to go together, but there are many exceptions, which have contributed to the confusion in terminology. For example, the term ''atypical carcinoid'' is sometimes used to indicate an aggressive tumor without secretions, whether anaplastic or well-differentiated.
In 2000, the World Health Organization (WHO) revised the classification of GEP-NETs, abandoning the term ''carcinoid'' in favor of ''neuroendocrine tumor'' (NET) and abandoning ''islet cell tumor'' or ''pancreatic endocrine tumor'' for ''neuroendocrine carcinoma'' (NEC). Judging from papers published into 2006, the medical community is accepting this new terminology with great sluggishness. (Perhaps one reason for the resistance is that the WHO chose to label the least aggressive subclass of neuroendocrine neoplasm with the term&nbsp;&ndash; ''neuroendocrine tumor''&nbsp;&ndash; widely used previously either for the superclass or for the generally aggressive noncarcinoid subclass.)
Klöppel ''et alia'' have written an overview that clarifies the WHO classification and bridges the gap to the old terminology (Klöppel, Perren, and Heitz 2004). In this article we conform to the old terminology.
====Summary of classification by cell characteristics (the WHO classification)====
* Superclass:
** Öberg, WHO, Klöppel ''et alia'': Gastro-entero-pancreatic neuroendocrine tumor (GEP-NET)
* Subclass 1 (less malignant)
** Öberg: Carcinoid
** WHO: Neuroendocrine tumor (NET)
** Klöppel ''et alia'': Well-differentiated neuroendocrine tumor (NET) (carcinoid)
** this article: Carcinoid
* Subclass 2 (more malignant)
** Öberg: Endocrine pancreatic tumor
** WHO: Neuroendocrine carcinoma (NEC)
** Klöppel ''et alia'': Well-differentiated neuroendocrine carcinoma (NEC) (malignant carcinoid)
** this article: Pancreatic endocrine tumor (PET) or endocrine pancreatic tumor (EPT) or islet cell tumor or noncarcinoid GEP-NET
* Subclass 3 (most malignant)
** WHO: Poorly-differentiated neuroendocrine carcinoma
** Klöppel ''et alia'': Poorly-differentiated neuroendocrine carcinoma (high-grade malignant carcinoid)
* Subclass 4 (mixed)
** WHO: Mixed endocrine/exocrine tumor
* Subclass 5 (miscellaneous)
** WHO: Rare neuroendocrine-like lesions
GEP-NETs are also sometimes called ''APUDomas'', but that term is now considered to be misleading, since it is based on a discredited theory of the development of the tumors.
<ref>
"The APUD concept led to the belief that these cells arise from the embryologic neural crest. This hypothesis eventually was found to be incorrect" (Warner 2005, 2).
<p>
"The APUD-concept is currently abandoned" (Öberg 1998, 2, [http://theoncologist.alphamedpress.org/cgi/reprint/3/5/339.pdf]).
</ref>




Revision as of 14:35, 20 August 2019


Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]; Associate Editor(s)-in-Chief: Sara Mohsin, M.D.[3]


Neuroendocrine tumors, or more properly gastro-entero-pancreatic or gastroenteropancreatic neuroendocrine tumors (GEP-NETs), are cancers of the interface between the endocrine (hormonal) system and the nervous system.

Historical Perspective

Siegfried Oberndorfer, in 1907, was the first person to distinguish clearly what we now call GEP-NETs from other forms of cancer. He gave the term "carcinoid" to these tumors, because they were so slow-growing that he considered them to be "cancer-like" rather than truly cancerous. In 1929, he reported that some such tumors were not so indolent – these he distinguished as what we now call PETs from what most authorities call carcinoids. Despite the differences between the two categories, some doctors, including oncologists, persist in calling all GEP-NETs "carcinoid", even into the twenty-first century. [1]

The earliest synthetic form of somatostatin used in the treatment of Neuroendocrine tumors was octreotide, first marketed, by Sandoz as Sandostatin, in 1988.

Classification

Human GEP-NETs by Site of Origin and by Symptom

Classification of GEP-NETs by cell characteristics

The diverse and amorphous nature of GEP-NETs has led to a confused, overlapping, and changing terminology. In general, aggressiveness (malignancy), secretion (of hormones), and anaplasia (dissimilarity between tumor cells and normal cells) tend to go together, but there are many exceptions, which have contributed to the confusion in terminology. For example, the term atypical carcinoid is sometimes used to indicate an aggressive tumor without secretions, whether anaplastic or well-differentiated.

In 2000, the World Health Organization (WHO) revised the classification of GEP-NETs, abandoning the term carcinoid in favor of neuroendocrine tumor (NET) and abandoning islet cell tumor or pancreatic endocrine tumor for neuroendocrine carcinoma (NEC). Judging from papers published into 2006, the medical community is accepting this new terminology with great sluggishness. (Perhaps one reason for the resistance is that the WHO chose to label the least aggressive subclass of neuroendocrine neoplasm with the term – neuroendocrine tumor – widely used previously either for the superclass or for the generally aggressive noncarcinoid subclass.)

Klöppel et alia have written an overview that clarifies the WHO classification and bridges the gap to the old terminology (Klöppel, Perren, and Heitz 2004). In this article we conform to the old terminology.

Summary of classification by cell characteristics (the WHO classification)

  • Superclass:
    • Öberg, WHO, Klöppel et alia: Gastro-entero-pancreatic neuroendocrine tumor (GEP-NET)
  • Subclass 1 (less malignant)
    • Öberg: Carcinoid
    • WHO: Neuroendocrine tumor (NET)
    • Klöppel et alia: Well-differentiated neuroendocrine tumor (NET) (carcinoid)
    • this article: Carcinoid
  • Subclass 2 (more malignant)
    • Öberg: Endocrine pancreatic tumor
    • WHO: Neuroendocrine carcinoma (NEC)
    • Klöppel et alia: Well-differentiated neuroendocrine carcinoma (NEC) (malignant carcinoid)
    • this article: Pancreatic endocrine tumor (PET) or endocrine pancreatic tumor (EPT) or islet cell tumor or noncarcinoid GEP-NET
  • Subclass 3 (most malignant)
    • WHO: Poorly-differentiated neuroendocrine carcinoma
    • Klöppel et alia: Poorly-differentiated neuroendocrine carcinoma (high-grade malignant carcinoid)
  • Subclass 4 (mixed)
    • WHO: Mixed endocrine/exocrine tumor
  • Subclass 5 (miscellaneous)
    • WHO: Rare neuroendocrine-like lesions

GEP-NETs are also sometimes called APUDomas, but that term is now considered to be misleading, since it is based on a discredited theory of the development of the tumors. [2]



Reference

  1. ↑ "The term 'carcinoid' was introduced by S[iegfried] Oberndorfer in 1907 to distinguish carcinoids as less rapidly growing and well-differentiated epithelial tumors of the small intestine from the more aggressively growing adenocarcinoma of the gut.... Strictly speaking ... the term 'carcinoid' [is] reserved for endocrine tumors of the gastrointestinal tract ... and not for those of the pancreas.... The vagueness of the term 'carcinoid' results from its histological features which are almost identical with those of endocrine pancreatic tumors" (Arnold et al. 2004, 195).

    "During his tenure at the Pathological Institute of the University of Munich, Oberndorfer noted in 1907 that the lesions were distinct clinical entities and named them 'karzinoide' ('carcinoma-like'), emphasizing in particular their benign features. In 1929 he amended his classification to include the possibility that these small bowel tumors could be malignant and also metastasize" (Modlin 2004).

    Regarding the persistence of the term carcinoid: on a PET news forum, a patient says "for over 4 yrs I was referred to as carcinoid. In fact even when it was discovered I was actually islet cell and the pathologist was questioned by my doctor (specialist in NET) about this the pathology said we classify all islet cell as carcinoid. Since then no matter how many times I say islet cell to a local doctor - oncologist, gastroendocrineologist, radiologist - you get the idea - they ALL continue to refer to me as carcinoid" (NET_IsletCell 2006).

  2. ↑ "The APUD concept led to the belief that these cells arise from the embryologic neural crest. This hypothesis eventually was found to be incorrect" (Warner 2005, 2).

    "The APUD-concept is currently abandoned" (Öberg 1998, 2, [1]).

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