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Neuroendocrine Tumours (NET)

Overview

Neuroendocrine tumours arise from special type of cells, called neuroendocrine cells, located within the intestine. These cells are like nerve cells and hormone-making endocrine cells. Neuroendocrine tumours can arise in any part of the body and are rare tumours. Conventionally they are slow-growing and behave differently from the traditional cancers.

Neuroendocrine tumours can form in any part of the body including the lungs and respiratory tract. Neuroendocrine tumours of the intestinal tract may arise from the

  • Small intestine – duodenum, jejunum and ileum
  • Stomach
  • Appendix
  • Large intestine – colon
  • Rectum
  • Pancreas

The tumours may arise from specialised cells, which secrete specific chemicals (hormones). And the over secretion of these hormones can result in specific symptom complexes (syndromes), which can be attributed to the action of these hormones. Tumours associated with over secretion of these hormones and specific syndromes are called “Functioning tumours”. There are neuroendocrine tumours, which do not secrete specific hormones and are referred to as “Non-functioning tumours”.

Depending on their biology and aggressiveness, neuroendocrine tumours are classified into Grades 1, 2, and 3.

Grade 1 and 2 tumours are more benign and slow-growing. Grade 3 tumours are also called as ‘Neuroendocrine Carcinomas (NEC)’ and are known to be locally aggressive and spread to other organs. 

The exact cause of NET is not fully known. The chances of tumour development increases in the following cases:

  • Genetic mutation: Variations in the genes and a family history increases the risk
  • Pre-existing conditions such as diabetes and peptic ulcer
  • Rare inherited diseases such as neurofibromatosis, multiple endocrine neoplasia and Von Hippel-Lindau syndrome

The symptoms differ based on functioning and non-functioning neuroendocrine tumours.

  • Functioning neuroendocrine tumours

    These secrete hormones which give rise to specific symptoms, based on the hormone secreted. Diagnosis is mainly based on clinical suspicion. Most common types include:

    • Insulinoma: Secondary to over-release of insulin from the pancreas, this leads to recurrent and repeatedly low sugar levels, thereby leading to symptoms of hypoglycaemia, and neurological symptoms due to constant low blood sugar.
    • Gastrinoma: This is due to over secretion of acid in stomach. Normal gastric acid secretion leads to digestion of the ingested food and absorption in the stomach. However, when gastric acid is released in excessive amounts, this results in severe acidic symptoms, development of “stomach like” ulcers in the large intestine, small intestine, and food pipe (oesophagus). The lesion causing gastrinoma may be present within the pancreas or even in the small intestine (duodenum).
    • Carcinoid tumour: This is due to the release of another chemical–5 hydroxy tryptamine (5 HT)–this hormone typically causes diarrhoea, flushing, and intermittent abdominal pain

  • Non-functioning tumours

    These do not produce symptoms by virtue of over secretion of hormones, as hormones are not secreted by them. However they may produce the following symptoms:

    • Bleeding: presents as blood in vomit or dark stools– Malena. Often, patients simply present with anaemia (low haemoglobin) and further investigations lead to a diagnosis of tumour
    • Abdominal pain
    • Loss of appetite and weight loss

  • Blood tests: Specific blood tests aim to identify elevated levels of the hormones in the blood, such as insulin, gastrin, chromogranin, etc.
  • CT scan and imaging: Neuroendocrine tumours may be incidentally discovered during an ultrasound or CT scan performed for other reasons. Tumours have a characteristic appearance, which can raise suspicion of pancreatic neuroendocrine tumours.
  • DOTA scan: This is a specialised type of nuclear medicine scan, specific and sensitive for neuroendocrine tumours (NETs). The presence of dye uptake confirms the presence of a tumour.

  • Surgery remains the mainstay of treatment for all neuroendocrine tumours.

    Depending on the location of the tumour, the operation indicated would include removal of the affected organ with an adequate surrounding tissue (margin), which may include:

    • Pancreatic surgery: Whipple procedure or distal pancreatectomy
    • Small bowel: Removal of a segment of intestine
    • Stomach: A part or portion affected by the tumour is removed from the stomach. Also known as Gastrectomy.
    • Colectomy: Part of the large intestine is removed
    • NETs may also spread to other parts of the body – e.g. liver.
    • Where possible all attempts to remove the part of the liver bearing the tumour should be performed. This is potentially curative and has achieved very good long-term results.
  • Small asymptomatic non-functioning NETs may be kept under observation and surveillance only after thorough investigation and discussion.
  • Non-surgical therapy
    • Chemotherapy: When surgery is not possible, certain medications are available, which will slow down the progression of the disease and also control the symptoms.
    • Somatostatin analogues: These causes inhibition of release of the hormones and hence, help in controlling the symptoms. The somatostatin analogues also prevent the spread of tumour.
    • Ablation: Radiofrequency ablation or microwave ablation is performed on the disease that spread to the liver or any other organ (e.g. lung).
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