With pancreatic neuroendocrine neoplasms, neuroendocrine refers to pancreatic cells
which release hormones in response to signals from the nerves, and neoplasm refers to a
cancer.
So, pancreatic neuroendocrine neoplasm is a cancer of neuroendocrine cells that are
within the pancreas.
They can also be called pancreatic neuroendocrine tumors, or just panNETs for short.
In addition to endocrine cells, the pancreas also has exocrine cells, which make up a majority
of the gland.
Most pancreatic cancers arise from exocrine cells and they're called adenocarcinomas,
whereas only a minority arise from panNETs.
Now, the pancreas is a long, skinny gland the length of a dollar bill which sits to
the left of the duodenum and behind the stomach, in the upper abdomen, or the epigastric region.
It plays two main roles - there's the exocrine part of the pancreas which has acinar cells
that make digestive enzymes that are secreted into the duodenum to help digest food.
There's also the endocrine part of the pancreas which has a few different types of islet cells,
or neuroendocrine cells, each of which make different hormones.
These neuroendocrine cells are present in clusters, or islands, called islets of Langerhans.
The largest group of cells are the beta (β) cells which secrete insulin.
Insulin mainly lowers the blood glucose levels by transporting glucose into the cells, and
also pushes potassium into cells, which decreases potassium in the blood.
Another group are the alpha (α) cells which secrete glucagon, it raises the blood glucose
levels by getting the liver to generate glucose from amino acids and lipids, and to break
down glycogen into glucose.
There are also delta (δ) cells which secrete somatostatin, which decreases the release
of other hormones, including insulin, glucagon, and serotonin.
There are also gamma (γ) cells, also called pancreatic polypeptide cells, which secrete
pancreatic polypeptide, which stimulates the release of digestive enzymes from the stomach
and small intestine, as well as slow down intestinal movement.
Finally, there are a few rare cell types called enterochromaffin cells, as well as D1 cells,
and G cells, which are scattered in the islets of Langerhans.
Enterochromaffin cells secrete serotonin, which helps with motility of the gastrointestinal
tract.
D1 cells release a hormone, vasoactive intestinal polypeptide or VIP, which relaxes the small
intestine and stimulates the release of intestinal digestive enzymes, but inhibits hydrochloric
acid release from the stomach.
G cells are found in the pancreas and stomach, and the secrete gastrin.
Gastrin stimulates the parietal cells in the stomach mucosa to secrete hydrochloric acid,
and also stimulates the glands in the epithelial layer.
In pancreatic neuroendocrine neoplasms, one of the many types of neuroendocrine cells
mutates and starts dividing uncontrollably, forming a tumor over time.
Sometimes the mutation is in a tumor suppressor gene like PTEN and MEN1.
Tumor suppressor genes usually regulate cell growth, so when they mutate, the result is
uncontrolled cell growth.
Mutation of the MEN1 gene results in an inherited condition known as multiple endocrine neoplasia,
or MEN, type I, where adenomas or malignant tumors form in the parathyroid gland, pituitary
gland, and pancreas.
Some PanNETs are benign tumors which means that they don't invade nearby tissues, whereas
others are malignant tumors meaning that they do invade surrounding tissues and even metastasize
or spread through the lymph to distant ones.
PanNETs are classified into functional tumors, which secrete hormones, and non-functional
tumors, which don't secrete any hormones.
Non-functional panNETs are more common, and they're usually asymptomatic until they
grow to a large size and metastasize to other organs like the liver.
Large tumors can compress surrounding structures, for example, a tumor might compress the common
bile duct, leading to a backup bile and causing obstructive jaundice, which is when the skin
turns yellow from the buildup of bilirubin in the tissues.
Functional panNETs are less common and depend on the type of cell they arise from and the
hormone they produce.
The most common functional panNET is an insulinoma which arises from β cells that make insulin.
Insulinomas are usually benign solitary tumors that cause hypoglycemia, or low blood glucose,
and in severe cases can lead to confusion and loss of consciousness.
The second most common type is a gastrinoma that arises from the G cells that make gastrin.
Gastrinomas secrete large amounts of gastrin, which results in excess hydrochloric acid
secretion, which produces a syndrome called Zollinger-Ellison syndrome.
Excess hydrochloric acid erodes the mucosa, which results in peptic ulcers.
A unique feature of Zollinger-Ellison syndrome is that the peptic ulcers are formed not only
in the stomach, and duodenum, but there's so much acid that ulcers are also formed in
more distant parts of the small intestine like the jejunum.
The acid also inactivates the pancreatic digestive enzymes, which allows food, especially fat
to pass right through the intestines undigested, leading to greasy and smelly stools—called
steatorrhea.
The third most common type of panNETs is a VIPoma which arises from the D1 cells that
make vasoactive intestinal peptide.
VIPomas result in WDHA syndrome, where WD stands for watery diarrhea, which is due to
increased fluid secreted by the small and large intestine, H stands for hypokalemia,
or low potassium levels in the blood due to potassium losses in the intestinal fluid,
and A stands for achlorhydria, the absence of hydrochloric acid secretion.
The fourth type is the glucagonoma which arises from the α cells that make glucagon.
Excess glucagon leads to increased blood glucose, resulting in diabetes mellitus.
Glucagonomas also result in a loss of lipids and proteins that are used to form glucose,
and they typically cause a necrolytic migratory erythema, which is a red blistering rash that
mostly affects the mouth and limbs.
The fifth type is a somatostatinoma that arises from δ cells which secrete somatostatin.
The excess somatostatin inhibits release of other pancreatic hormones, like insulin, gastrin
and VIP; which leads to diabetes mellitus, steatorrhea, and hypochlorhydria, or decreased
hydrochloric acid secretion.
Finally, there are also panNETs that develop from pancreatic polypeptide cells and enterochromaffin
cells, but these are very rare.
Diagnosis of functional panNETs is based on measuring pancreatic hormone levels.
Non-functional tumors are usually hard to detect since no increase hormone levels can
be found in the blood.
In addition, MRI or CT imaging of the pancreas can help identify a tumor and estimate its
size.
The treatment for a panNETs depends on the type and size.
When dealing with a functional tumor, with the exception of somatostatinomas, somatostatin-like
medications are given to reduce hormone production.
In addition, gastrinomas can be treated with medications that block gastric acid secretion.
When dealing with nonfunctional panNETs, large tumor that cause compression can be managed
with surgery.
All right, as a quick recap, pancreatic neuroendocrine neoplasms, or panNETs, are tumors of hormone
producing cells of the pancreas, and their symptoms depend on their size and cellular
origin.
PanNETs can be non-functional tumors, meaning they don't produce any hormones, or they can
be functional tumors, meaning they produce hormones.
The most common types of functional tumors include insulinomas that make insulin, gastrinomas
that make gastrin, glucagonomas that make glucagon, VIPomas that make vasoactive intestinal
peptide, and somatostatinomas that make somatostatin.
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