What is APUDoma (neuroendocrine tumors)?
APUDomas, now referred to as neuroendocrine tumors (NETs), are a varied group of tumors that originate from the wide-ranging neuroendocrine system, mainly in the gastrointestinal tract and lungs. Although each tumor may present with features specific to the organ it affects, they all share certain unique traits, regardless of where they originate. Even though these types of tumors aren’t very common, their occurrence has been gradually increasing over time.
Over the past decade, significant advancements have been made in the methods used to diagnose and treat these tumors, due mostly to improved understanding of their molecular biology. When the tumors are localized, surgery is usually the preferred treatment option. However, for more advanced NETs, therapies that act on the entire body, also known as systemic therapies, are considered.
What Causes APUDoma (neuroendocrine tumors)?
APUDomas, also known as APUD tumors, come from a specific type of cell known as APUD cells. These cells are unique because they have the capability to absorb certain types of substances (amine precursors), change them into a different form (through decarboxylation), and then turn them into active amines. This process gives them their name: APUD stands for amine precursor uptake and decarboxylation.
The first description of these cells was by Pearse in the 1960s, who claimed that they came from the neural crest, a specific part of the embryo. However, this idea was later proved wrong. It’s now believed that APUD cells come from versatile cells known as multipotent stem cells, which can grow into many different types of cells. These stem cells are then implanted in various parts of the body, which helps spread our body’s endocrine system, a network that controls hormones.
Even though researchers have sponsored countless studies on these tumors, the exact cause of NETs (a type of tumor that can come from APUD cells) is still unclear. There are, however, several factors that could increase the risk, such as smoking, genetic abnormalities, and changes in the immune system.
Risk Factors and Frequency for APUDoma (neuroendocrine tumors)
NETs, or Neuroendocrine Tumors, are a type of cancer that can start in different parts of the body. Over half of these cancers start in the gastrointestinal tract and pancreas, while around a quarter begin in the bronchopulmonary tree, which is a fancy term for the airways of your lungs. Some other places these tumors can start include the thymus (a part of your immune system), breasts, prostate, and skin. As of 2014, there were around 171 thousand people in the US with NETs, and each year about 3.56 in every 100,000 people will be diagnosed with this type of cancer.
The number of people being diagnosed has gone up in the past 30 years because we’ve gotten better at finding these tumors. Interestingly, it’s been observed that more Black people get this type of cancer than white people. If one of your parents, brothers, or sisters has had this type of cancer, you are three times more likely to get it yourself.
- Over half of NETs start in the gastrointestinal tract and pancreas.
- About a quarter of NETs begin in the bronchopulmonary tree.
- NETs can also start in the thymus, breasts, prostate, and skin.
- As of 2014, around 171,321 people in the US had NETs.
- Every year, about 3.56 in every 100,000 people are diagnosed with NETs.
- The number of new diagnoses has been increasing over the past 30 years due to better detection techniques.
- Black people are more likely to get NETs than white people.
- If your parent, brother, or sister has had NETs, you are three times more likely to get it.
Signs and Symptoms of APUDoma (neuroendocrine tumors)
Neuroendocrine tumors (NETs) typically occur randomly, but they can also be a part of inherited conditions such as multiple endocrine neoplasia type 1 (MEN-1). This inherited condition includes the development of tumors in the pituitary gland, parathyroid glands, and pancreas. Depending on whether these tumors secrete hormones, they can show symptoms (functioning) or remain unnoticed (non-functioning). These NETs can develop in various organs and from different cell types. They are usually categorized into two types: NETs in the gastrointestinal tract, known as carcinoid tumors, and pancreatic NETs.
Carcinoid tumors in the gastrointestinal tract are known for releasing a large amount of vasoactive peptides and amines, such as serotonin and tachykinins into the blood. This leads to a condition known as carcinoid syndrome, which can present symptoms like skin flushing, diarrhea, abdominal pain, or even difficulty in breathing. However, these symptoms typically occur if the tumors have spread to the liver or other parts of the body. Moreover, long-term exposure of the heart to these active peptides can lead to carcinoid heart disease, characterized by a thickened heart lining.
On the other hand, pancreatic NETs can lead to a variety of symptoms based on the type of hormones they secrete. For instance, pancreatic NETs which secrete insulin (insulinomas) can cause low blood sugar levels, which can be relieved by consuming glucose. Other types of pancreatic NETs could secrete hormones that lead to multiple digestive system ulcers, diabetes, dermatitis, blood clots, depression, and severe diarrhea.
- Carcinoid tumors cause carcinoid syndrome, characterized by:
- Skin flushing
- Diarrhea
- Abdominal pain
- Difficulty in breathing
- Over time, carcinoid tumors can cause thickening of the heart lining
- Pancreatic NETs cause symptoms based on the hormones they secrete, such as:
- Low blood sugar levels (with insulinomas)
- Digestive system ulcers, diarrhea, and abdominal pain (with gastrinomas)
- Diabetes, dermatitis, blood clots, and depression (with glucagonomas)
- Severe diarrhea (with VIPomas)
Testing for APUDoma (neuroendocrine tumors)
Diagnosing neuroendocrine tumors (NETs) involves various steps, including carefully checking a person’s medical history and carrying out a physical examination. It can also involve checking hormone levels, carrying out imaging tests like CT scans or MRIs, and confirming the diagnosis through tests on tissue samples.
For example, if your doctor suspects you might have carcinoid syndrome (which is linked with some types of NETs), he or she might suggest a test to measure the levels of 5-hydroxyindoleacetic acid (5-HIAA) in your urine or blood. This substance is what remains after your body metabolizes serotonin, a hormone that’s often produced in large quantities by certain NETs. This test has been found to be fairly accurate at predicting whether this type of NET is present.
For people potentially suffering from pancreatic NETs (pNETs), different tests can be carried out to measure specific hormone levels in the blood. For example, if you might have a gastrinoma (a type of pNET), your doctor might suggest a test to measure your fasting gastrin blood level. Remember: if you have a pNET, you might also need to be evaluated for multiple endocrine neoplasia (MEN) type 1 tumors of the pituitary and parathyroid glands.
When it comes to imaging, methods like CT and MRI scans can be used to reveal the size and location of these tumors. Some tumors that develop in the gastrointestinal tract or pancreas (GEP-NETs) show somatostatin receptors on their surfaces. Because of this, these receptors can be targeted by a radioactive substance called octreotide, which can bind to these receptors, making the tumors detectable. But note that, insulinomas (a type of NET) often express fewer somatostatin receptors.
A positron emission tomography (PET) scan using a substance called gallium-DOTATOC might be used instead due to its higher level of sensitivity. However, this scan is not available everywhere.
Treatment Options for APUDoma (neuroendocrine tumors)
Diverse methods exist to deal with diverse types of tumors. The only way to entirely cure these tumors is through surgical removal, a method generally used on tumors that haven’t spread widely. However, surgery can also help relieve symptoms by cutting down the size of the tumor. Because most of these tumors are not identified until after they’ve metastasized or spread, aggressive and high-grade tumors are often treated with chemotherapy.
For patients with liver tumors, other treatments include procedures that block the blood supply to the tumor, such as trans-arterial embolization, or chemical or radiation treatments delivered directly to the tumor. Additionally, medications that slow tumor growth, like somatostatin analogs or low-dose interferon, are approved treatments for slow-growing and intermediate tumors.
What else can APUDoma (neuroendocrine tumors) be?
- Irritable Bowel Syndrome (a common disorder affecting the large intestine)
- Cancerous tumors in the small intestine
- Medullary Thyroid Carcinoma (a rare form of thyroid cancer)
- Systemic Mastocytosis (a disorder causing an excess of mast cells in the body)
- Lung cancers
Surgical Treatment of APUDoma (neuroendocrine tumors)
The only treatment that could potentially cure localized and locally advanced neuroendocrine tumors (NETs) is surgery. For pancreatic NETs (pNETs) larger than 2 cm, symptomatic, or of low to intermediate grade, procedures such as pancreaticoduodenectomy (Whipple surgery) and distal pancreatectomy are usually performed. However, the surgical removal of less severe pNETs—those less than 2 cm, non-functioning, and low-grade—is a topic of ongoing debate.
In cases where pNETs are surgically removed and found to be poorly differentiated, platinum-based chemotherapy is typically recommended after surgery. If the tumor is too large for surgical removal, a debulking surgery, which reduces tumor size, is suggested.
Even for midgut NETs that are small and produce no symptoms, surgery is often the preferred method of treatment. Right hemicolectomy is typical for tumors around the ileocecal valve or tumors in the small intestine that are larger than 2 cm. If the tumors are in the appendicitis and less than 1 cm, a simple appendectomy usually suffices. But for less than 1 cm tumors in the small intestine, a small intestinal resection is generally required.
Something to note is that carcinoid crisis can be a complication that occurs during surgery for carcinoma syndrome. This can be triggered by factors such as anesthesia, epinephrine, and handling of the tumor. Therefore, prior to surgery, any patient should receive a dose of octreotide, administered subcutaneously or intravenously, 1 to 2 hours before the procedure to reduce the risk of this complication.
What to expect with APUDoma (neuroendocrine tumors)
The survival rates for neuroendocrine tumors (NETs) can differ greatly depending on where the tumor first forms. Tumors starting in the rectum tend to have the best outlook. In contrast, pancreatic neuroendocrine tumors (pNETs) usually have the worst outlook—this is because pancreatic tumors often spread to other parts of the body by the time they’re diagnosed. The location of the initial tumor is one of the most reliable ways to predict a patient’s outcome when dealing with NETs.
Possible Complications When Diagnosed with APUDoma (neuroendocrine tumors)
Common Health Issues:
- Carcinoid heart disease
- Mesenteric fibrosis
- Psychiatric disorders
- Carcinoid crisis
- Skin and lung scarring and pellagra
Preventing APUDoma (neuroendocrine tumors)
The main focus of educating patients should be to help them understand the potential long-term problems they may encounter relating to bowel and bladder control. Neuroendocrine tumors (NETs) may cause symptoms or remain quiet, and this depends on whether they secrete hormones. These tumors can start in various organs and from different types of cells. There are several ways to handle these varied tumors. The only treatment that can fully cure these tumors is surgical removal. However, there are different treatment methods used for more advanced diseases.
