neuroendocrine tumor
Scattered throughout the body — lining the gut, dotting the lungs, hiding in the pancreas — are hormone-secreting cells that behave a bit like both nerve cells and gland cells. A neuroendocrine tumor is a growth of these cells. Because the cells themselves are spread out rather than gathered into one organ, these tumors can crop up in many different places.
Like other endocrine tumors, they may or may not secrete. A functional neuroendocrine tumor releases active hormones and announces itself through their effects; a non-functional one may grow quietly until it causes a local problem or is found incidentally. What unites them is a shared cell biology and a tendency to make hormone-storing granules, which is why they often respond to drugs that mimic the body's natural brake on hormone secretion.
Their behavior ranges widely, from slow-growing tumors a person may live with for years to fast, aggressive cancers. Pathologists grade them by how quickly the cells divide, which helps predict their course. Because many carry receptors for somatostatin, imaging and treatment can be targeted to those receptors — a notable example of using a tumor's own endocrine nature against it.
A small bowel neuroendocrine tumor secreting serotonin may grow slowly for years; once it spreads to the liver and floods the bloodstream, it can cause the flushing and diarrhea of carcinoid syndrome.
Often indolent, sometimes hormone-active.
These cells belong to the diffuse endocrine system, hormone cells dispersed through other organs rather than packed into a dedicated gland; carcinoid tumors of the gut are a well-known type of neuroendocrine tumor.