Neuroendocrine tumors

Neuroendocrine tumors grow from neuroendocrine cells, which work like the body's mail carriers: they send and receive messages through hormones, chemicals that carry signals that keep the body working. These tumors often grow very slowly, and in adults they show up most often in the digestive tract, the path food travels through.

Here is what goes on inside. Some of those cells pick up mutations, which are changes in their genes, and their signaling pathways, the cell's internal message routes, get thrown off. The result is that the cells multiply out of control. Some of these tumors, called functional tumors, also make too much of certain messenger substances, such as serotonin or gastrin. Think of a faucet left running: a message that should come out in just the right amount comes gushing out, and that excess causes syndromes, meaning groups of symptoms that show up together, such as carcinoid syndrome.

These tumors can also arise in the pancreas, a gland made up of different kinds of cells: exocrine cells, which make juices for digestion, and endocrine cells, which make hormones. A pancreatic neuroendocrine tumor starts in the endocrine cells. It is less common than cancer that starts in the exocrine cells, but here is the key point: it has a better prognosis, meaning its expected course is more favorable.