Types of cancer

Neuroendocrine tumors

Neuroendocrine tumors are rare and can be found in most organs, including the lungs and pancreas. They are more common in people aged 50 to 60 years. There is no way to prevent the disease, as its cause is unknown. Know more.
5 min read
per: Grupo Oncoclínicas
Neuroendocrine tumors
Winth an incidence of seven in every 100 thousand people, neuroendocrine tumors are more common in men and women between 50 and 60 years.

What are neuroendocrine tumors

Neuroendocrine tumors (NET) are rare types of cancer that originate in the cells of the neuroendocrine system. These cells spread throughout the body and are found in most organs, including the gastrointestinal tract, pancreas, thyroid, and lungs.

Neuroendocrine cells are like nerve cells, but they also produce hormones, like cells in the endocrine system.

When neuroendocrine cells change and do not grow or function normally, they can lead to the formation of neuroendocrine tumors. Some are detected and treated quickly, others manage to spread to other parts of the body. They can evolve slowly (indolent) or quickly (aggressive).

With an incidence of seven in every 100 thousand people, neuroendocrine tumors are more common in men and women aged between 50 and 60 years.

Subtypes of neuroendocrine tumors

First, it is important to note that neuroendocrine tumors that produce hormonal symptoms are called “functioning”, while those asymptomatic regarding hormonal symptoms are “non-functioning”.

There are three main types of neuroendocrine tumors. Here they are:

Gastrointestinal neuroendocrine tumors (GI NETs) – is the most common type. As the name implies, they are tumors found in the gastrointestinal tract, which develop in organs such as the small intestine, rectum, stomach, colon, esophagus and appendix. Most are indolent, that is, they progress slowly. The most common are in the small intestine and release serotonin mainly when they metastasize to the liver.

The GI NETs gain two subdivisions, related to the comparison with normal cells:

  • Well-differentiated GI NETs: these are composed of cells that look and act like normal cells. They can be both indolent and aggressive; are classified as grade 1 and 2 tumors, in the most indolent cases, and grade 3 in the fastest growing cases with higher proliferation rates;
  • Poorly differentiated GI neuroendocrine carcinomas: these are aggressive tumors composed of very abnormal cells, with a behavior and treatment completely different from other tumors.

Pulmonary neuroendocrine tumors – responsible for a quarter of NETs, ​​they develop in the lungs or airways, often in the bronchi. There are four subtypes of pulmonary NETs:

  • Typical carcinoid tumors: these are indolent and have cells that look and act like normal cells;
  • Atypical carcinoid tumors: these are like typical carcinoid tumors but are more likely to spread to other parts of the body.
  • Large cell and small cell lung neuroendocrine carcinomas: these are composed of very abnormal cells, tend to be aggressive and to spread to other parts of the body more quickly;
  • Pancreatic neuroendocrine tumors: these are tumors very similar to the pancreatic islets (group of cells in the pancreas that produce the hormones glucagon, insulin and somatostatin)5. They are subdivided into two groups: Functional Pancreatic Neuroendocrine Tumors and Nonfunctional Pancreatic Neuroendocrine Tumors. They can release hormone, but do not cause the syndrome associated with it.

Other rare NETs are those that start at:

  • Thyroid gland – medullary thyroid tumors;
  • Skin – Merkel cells cancer;
  • Adrenal glands – pheochromocytoma;
  • Thymus;
  • Other organs such as breasts, prostate and kidneys.

In approximately 10% of cases it is not impossible to determine where the NET started. When this is so, it is called carcinoma of unknown primary (CUP).

Symptoms and signs of neuroendocrine tumors

Neuroendocrine tumors can be asymptomatic when indolent. Symptoms and signs tend to appear when tumors are aggressive and functional, and they vary by disease subtype.

Symptoms of gastrointestinal neuroendocrine tumors:

  • Abdominal discomfort or pain;
  • Sudden hot flashes with facial flushing (red face);
  • Chronic diarrhea;
  • Bleeding in the rectum or when defecating;
  • Anemia and fatigue;
  • Heartburn or indigestion;
  • Stomach ulcers, which cause heartburn, indigestion, and pain in the chest or abdomen;
  • Weight loss for no apparent reason;

Symptoms of lung neuroendocrine tumors:

  • Persistent cough;
  • Asthma attacks;
  • Coughing up blood;
  • Difficulty breathing;
  • Fatigue;
  • Pneumonia.

Symptoms of pancreatic neuroendocrine tumors:

  • Hypoglycemia, which can cause sweating, shakiness, dizziness, extreme hunger and lack of concentration;
  • Hyperglycemia, which can cause extreme thirst, frequent urination and diarrhea;
  • Stomach ulcers, which cause heartburn, indigestion, and pain in the chest or abdomen;
  • Weight loss for no apparent reason;
  • Red spots, which can sometimes cause itching and pain on the skin;
  • Jaundice;
  • Chronic diarrhea that is difficult to control, which can lead to dehydration.

Diagnosis of neuroendocrine tumors

Since they have symptoms very similar to those of other diseases, neuroendocrine tumors can have a delayed diagnosis for months and even years. It is not uncommon for patients to hear from doctors that what they feel is related to Irritable Bowel Syndrome, gastritis, asthma, hypertension and even menopause.

The accurate diagnosis is made by a doctor attentive to the existence of neuroendocrine tumors. When suspecting the presence of the disease, tests such as the ones on the list must be carried out:

  • Physical examination and personal and family medical history;
  • Biopsy (taking a sample of tissue where a tumor is suspected for analysis);
  • Blood and urine tests;
  • Imaging tests such as ultrasound, CT scan, digestive endoscopy and endoscopic ultrasound, echocardiogram and nuclear magnetic resonance (to look for clues about a medical condition in the body that leads to tumors);
  • Octreotide or MIBG-labeled scintigraphy tests, PET CT (positron emission tomography) labeled with somatostatin analogues (specific tests for cases with a confirmed diagnosis of NET);
  • Staging tests, such as bone scans and CT scans (to determine where NETs started and whether they are spread throughout the body);
  • Extra tests, such as bronchoscopy and pulmonary function tests (to confirm other suspicions related to NETs).


The treatment of neuroendocrine tumors depends on several factors, such as:

  • Where the cancer originated;
  • Whether the disease has spread throughout the body and where in it;
  • The characteristics of the disease (indolent or aggressive, functional or non-functional);
  • Other patient health conditions.

In most cases, surgery is the first choice of treatment. To alleviate symptoms and/or control tumor growth, specific medical treatments such as radiotherapy and chemotherapy are used.

If the tumor can be removed completely with surgery, there may be no need for further treatment. Even if the tumor has spread (that is, it has metastasized), surgery can still remove part of the tumor and any other secondary tumors – this is called tumor cytoreduction.

In cases where NETs are blocking an organ, such as the intestine, surgery can be helpful to relieve the blockage.

The most commonly used treatment in the case of well-differentiated neuroendocrine tumors is the somatostatin analogue, through an intramuscular or subcutaneous injection of a class of non-cytotoxic drugs, different from conventional chemotherapy. These drugs control both symptoms related to functional syndromes and the growth of tumor cells.

Radiotherapy is rarely used in the treatment of NETs, ​​but it can be used, for example, in some cases to control bone metastases.

Chemotherapy uses drugs delivered into the bloodstream to destroy cancer cells, usually by stopping the cancer cell’s ability to grow and divide. It can be used in cases of more aggressive or rapidly growing tumors with associated symptoms.

Immunotherapy still has its role under investigation in the fight against NETs, ​​but it has already demonstrated efficacy data in the most aggressive subtypes.


Since the causes of neuroendocrine tumors are unknown, it is not possible to take preventive measures against them.

However, in some rare cases NETs may be associated with the following rare familial syndromes:

  • Multiple endocrine neoplasia type 1 (MEN 1);
  • Neurofibromatosis type 1;
  • Von Hippel-Lindau Syndrome (VHL).

Keeping them under control may be a way to minimize the risk of developing neuroendocrine tumors.


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