Neuroendocrine tumors are a diverse family of neoplasms affecting many organs and tissues. Some are functional (ie, release a hormone product). Clinical signs vary, from syndromes of hormone excess to effects related to size and expansion of the tumor (mass effect). Neuroendocrine tumors may be found incidentally in the course of imaging studies or at necropsy. Treatment options vary, from surgical removal to medical treatment.
Neuroendocrine tumors comprise a family of tumors that arise from neuroendocrine cells.
Neuroendocrine cells are characterized by their ability to produce and secrete a neuromodulator, transmitter, or hormone. In addition, these cells contain dense core secretory granules, the storage site for the secreted products. Neuroendocrine cells can release their product in a regulated manner by classical exocytosis.
Neuroendocrine cells differ from classical neurons in that they lack axons and synapses.
Certain molecules, particularly those of the granin family (eg, chromogranin), are synthesized and stored in neuroendocrine cells and serve as immunohistologic markers.
Previously, neuroendocrine cells were classified as amine precursor uptake and decarboxylation (APUD) cells and were believed to be solely derived from neuroectoderm. However, more recent evidence supports a more diverse embryological origin.
Because of the diffuse distribution of cells, particularly within the GI tract, neuroendocrine tumors are found in a variety of locations. Examples of neuroendocrine tumors and the organ or tissue affected are summarized in the table.
Examples of Neuroendocrine Tumors
Tumor | Organ/tissue |
|---|---|
Carcinoids | GI tract |
Gastrinoma | GI tract |
Insulinoma | Pancreas |
Glucagonoma | Pancreas |
Pheochromocytoma | Adrenal |
Thyroid C-cell tumors (medullary carcinoma of the thyroid gland) | Thyroid |
Small cell lung cancer | Lung |
Multiple endocrine neoplasia | Several sites |
Merkel cell tumor | Skin |
Chemodectoma (carotid and aortic bodies) | Cardiovascular |
Overall, neuroendocrine tumors are rare tumors in humans and animals.
Some neuroendocrine tumors oversecrete their normal product, and the excessive levels result in the observed clinical signs. Insulinoma is an example and is the most common neuroendocrine tissue tumor in domestic species. Other neuroendocrine tumors are nonfunctional, and clinical signs instead result from physical forces associated with expansion or metastasis.
Neuroendocrine tumors are difficult to identify. They may be found incidentally in the course of imaging studies; however, some are identified only at necropsy.
Key Points
Insulinoma is the most common neuroendocrine tissue tumor in domestic species.
Some neuroendocrine tumors oversecrete their normal product, resulting in clinical signs; clinical signs of nonfunctional neuroendocrine tumors result from physical forces associated with expansion or metastasis.
Generally, neuroendocrine tumors are rare and difficult to identify.
