A 27 year old female named Clara comes to the clinic complaining of abdominal pain and watery diarrhea, which started three months ago. Since then, Clara has also noticed that from time to time, the skin of her face and neck suddenly turns red and feels warm, especially when she drinks alcohol or gets angry. On clinical examination, you notice that both Clara’s legs and feet look swollen. Next, you run a urine test which shows an increased level of 5-hydroxyindoleacetic acid. You then decide to order a CT scan, which reveals a large mass in the appendix, along with several smaller masses involving the liver. Some days later, you see a 65 year old male named William, who came in complaining of heartburn and abdominal pain for the past few months. He also states that his stools are often greasy and foul-smelling. Upon further questioning, William mentions that lately he’s lost around 15 kilograms or 33 pounds, although he hasn’t been exercising or dieting at all. The first thing you do is run a blood test, which reveals a serum gastrin level of 1400 picograms per milliliter. Then, you decide to perform an upper gastrointestinal endoscopy, during which you observe multiple ulcers in the stomach, duodenum, and jejunum.
Okay, based on the initial presentation, both Clara and William seem to have some form of neuroendocrine tumor of the gastrointestinal system. These tumors arise from neuroendocrine cells, which are most abundant in the epithelial layer of gastrointestinal tract. Other common locations are the thyroid gland with medullary thyroid cancer, the lungs, where small cell carcinoma can occur, and the medulla of the adrenal gland, which can give rise to pheochromocytoma.
Neuroendocrine cells get their name from the fact that they’re activated like neurons, since they can receive input from neurotransmitters released by other neurons, but they respond like endocrine cells by releasing hormones into the bloodstream. In a test question, neuroendocrine cells can also be called APUD cells, which stands for amine-precursor uptake decarboxylase cells. That’s because they can take up certain substances called amine precursors, such as DOPA and 5-hydroxytryptophan, and use an enzyme called decarboxylase to convert them to certain amine hormones, such as dopamine and serotonin.