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Neuroendocrine tumours (NETs) are abnormal growths found in the specialised cells called the neuroendocrine cells. These tumours are very rare and can be benign or malignant. Most of the reported cases are benign. The neuroendocrine cells are similar to the nerve cells and hormone-producing cells. NETs mostly develop in the intestine and are found in the pancreas, lung, appendix, small intestine, and rectum  .
NETs are of different types, depending upon the location of the tumour growth, but are treated as a group of tissue as the cells share similar features such as possessing special secretory granules and producing biogenic amines and polypeptide hormones . The condition develops in stages, with it being contained in a particular area of the body (localised), have spread to nearby tissues or lymph nodes (regional) and have spread throughout the body (metastatic).
Read on to know more about neuroendocrine tumours, the different types, its causes and so on.
Types Of Neuroendocrine Tumours
Classified as being functional or non-functional, functional NETs produce too much of a specific type of hormone whereas non-functional tumours may make hormones that do not cause any symptoms. The tumours can be indolent (tumour grows slowly) or aggressive (the tumours grow quickly and tend to spread to other parts of the body)  .
1. Gastrointestinal neuroendocrine tumours (GI NETs)
A common type of neuroendocrine tumour, GI NETs develop in the organs located in the gastrointestinal (GI) tract such as the small intestine, rectum, stomach, colon, oesophagus and appendix. Most commonly, it is found in the small intestine and causes the release of too much serotonin, leading to carcinoid syndrome. GI NETs are further classified by how different the cells are from normal cells (differentiation) and how fast cell growth is (grade).
It is classified into well-differentiated GI NETs and poorly differentiated GI neuroendocrine carcinomas.
2. Lung neuroendocrine tumours (lung NETs)
These are one of the most common types of neuroendocrine tumour which develops in the lungs or airways. They often develop in the bronchi as well. Lung NETs are further classified into four subtypes.
- Typical carcinoid tumours: These are indolent tumours found in the lungs, and the cells do not undergo any visible changes and look similar to that of normal cells. Typical carcinoid tumours tend to grow slowly.
- Atypical carcinoid tumours: These are well-differentiated cancerous tumours of the lung. Under this also, the cells look normal and do not undergo any drastic changes. Atypical carcinoid tumours tend to grow slowly but can spread to other parts of the body.
- Large cell lung neuroendocrine carcinomas: These are poorly differentiated cancerous tumours and have abnormal cancer cells. The tumours can be aggressive, causing its quick growth. They can spread to other parts of your body as well.
- Small cell lung neuroendocrine carcinomas: Also called as mall cell lung cancers, these are poorly differentiated cancerous tumours. The tumours are aggressive, grow quickly and may spread to other parts of the body.
3. Pancreatic neuroendocrine tumours (pNETs)
These tumours resemble the islet cells of the pancreas. pNETs are classified by examining the cells with the normal cells and recording the differences. It is also classified in accordance with the speed of cell growth.
- Well-differentiated pNETs: Under this, the cells resemble the normal cells and are indolent tumours that grow slowly.
- Poorly differentiated pancreatic neuroendocrine carcinomas: These are cancerous tumours with abnormal cells. They are aggressive and grow quickly.
Some of the other common types of neuroendocrine tumours are as follows  :
- Merkel cell carcinoma - a type of non-melanoma skin cancer
- medullary carcinoma - a type of thyroid cancer that starts in the C cells of the thyroid
- parathyroid cancer or parathyroid adenoma
- pituitary gland tumours
- pheochromocytoma - starts in the chromaffin cells of the adrenal glands
- paraganglioma - starts in the chromaffin cells outside the adrenal glands
- neuroendocrine tumours of the ovaries or testicles
- thymic neuroendocrine cancer
Symptoms Of Neuroendocrine Tumours
The signs that you may have developed a NET depends on the type and location of the tumour.
If the person is suffering from pancreatic NET, the symptoms will be as followed :
- Constant hunger
- Blurred or double vision
- Fast heartbeat
- Stomach pain
- Weight loss
If the individual is suffering from lung neuroendocrine tumours or carcinoid tumours, the symptoms will be as followed :
- Weight gain or loss
- Chest pain
- Red, warm, itchy skin, often on your face and neck
- Stomach pain
- Trouble breathing
- Feeling tired or sick
And the common symptoms of NETs are as followed :
- Nausea or vomiting
- Yellowish skin or eyes
- Anxiety attacks
- Weight gain or loss
- A fast heart rate
- Rapid pulse
- Night Sweats
- Appetite loss
- Hoarse voice
Causes Of Neuroendocrine Tumours
In various cases, there has been a lack of clarity in understanding what the real cause is. However, your chances of developing the disease are more if you have a history of the following diseases in your family  .
- Multiple endocrine neoplasia type 1, causes tumours to grow in the pancreas and other organs.
- Neurofibromatosis type 1, causes tumours in your adrenal glands.
- Von Hippel-Lindau syndrome causes the development of tumours and fluid-filled sacs form in many parts of your body.
Risk Factors Of Neuroendocrine Tumours
Some of the factors that can increase your chances of developing NETs are mentioned below .
- Hereditary conditions
- Family history of cancer
- Chronic atrophic gastritis
- Alcohol consumption
- Having a high body mass index (BMI) or being obese
- Following diets that are high in saturated fat, which includes eating red and processed meats
Diagnosis Of Neuroendocrine Tumours
The doctor will begin with a physical examination and ask you about any symptoms you have. Based on the physical examination, your doctor may refer you to a specialist or order tests to check for NETs  .
- Blood and urine tests: It will involve checking the levels of hormones in your body to see if they're too high or too low. An electrolyte panel and blood sugar test will be carried out.
- CT scan: Will help the doctor understand if tumours are present. And find out where the tumours are in those areas, find out if a NET has spread to the liver and determine whether surgery can be done.
- MRI: Using powerful magnets and radio waves, images of your internal organs will be taken. This will help the doctor understand the location of the tumours.
- Octreotide scan: It is a nuclear medicine imaging test that uses radioactive materials called radiopharmaceuticals to look for the presence of NET cells in the body.
Some of the other diagnosis methods are a biopsy, molecular testing, MIBG scan, PET scan, barium tests, endoscopy and a bone scan.
Treatments For Neuroendocrine Tumours
Depending upon certain factors, the precise treatment for NET will be determined by the doctor. Those factors are  :
- The kind of tumour you have and how many there are
- If it is cancerous or not
- If it has spread to other parts of your body
- Hormone therapy
- Embolization therapy
- Radionuclide therapy
- Targeted therapy
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