Neuroendocrine tumors (NETs) are cancers that originate from special cells called neuroendocrine cells. These cells share features of both nerve cells and hormone-producing cells. In response to signals from the nervous system, these cells release certain hormones into the blood.
NETs can develop anywhere in the body, but most common sites are the gastrointestinal tract, pancreas, rectum, lungs, or appendix. Although there are many types of NETs, they are mostly classified as:
Carcinoid tumors: These are NETs that most commonly arise in the GIT, lungs, appendix or thymus but can also grow in lymph nodes, brain, bone, gonads or skin.
Pancreatic NETs: NETs that typically arise in the pancreas and includes gastrinomas, insulinomas, VIPomas or glucagonomas.
Symptoms:
Symptoms depend on the tumor type, size, and location, hormone production (functional or non-functional) and extent of the spread to other parts of the body. Carcinoids, usually located in mid-gut, secrete an excess of hormones called serotonin which causes a constellation of symptoms called carcinoid syndrome that includes flushing, diarrhoea, asthma/wheezing, abdominal pain and palpitation. Usually, symptoms don't develop until the tumor spreads to the liver, which can make NETs very hard to diagnose.
Pancreatic neuroendocrine tumors (pNETs), also known as islet cell tumors may be associated with watery diarrhoea, diabetes mellitus, gastric ulcers or skin rash. Patients are usually asymptomatic unless the tumor causes obstruction resulting in jaundice or pain. Sometimes patients may experience gastrointestinal haemorrhage.
Diagnosis:
Depending on the tumor location, CT scan of chest, abdomen or pelvis is recommended. In case of low-grade NETs, functional imaging modality like Somatostatin receptor (SSR) based 68Ga-dotatate PET scan is preferred to rule out a distant spread and to assess whether the patient will benefit from SSR directed therapy. Measurement of the secreted hormones in the blood or their associated urinary products is done to aid in initial diagnosis or to monitor treatment response. The essential markers include Chromogranin A, Urine 5-hydroxy indole acetic acid, Neuron-specific enolase and Synaptophysin.
Treatment:
Surgery always is the primary treatment of choice for localised and resectable NETs irrespective of location and grade, followed by annual surveillance. SBRT can be considered in bronchopulmonary NETs if surgery is contraindicated. For pancreatic NETs pre-operative control of gastrin, insulin, glucagon or vasoactive intestinal peptide (VIP) secretion and correction of blood glucose and electrolyte (K+, Mg2+ and HCO3) imbalance is mandatory
For locally unresectable tumors the treatment depends on the location of tumor.
Bronchopulmonary NETs:
Observation can be considered for asymptomatic patients with low-grade tumours.
For patients with symptoms or a high tumour burden, targeted therapy agents like Everolimus is preferred. Octreotide or Lanreotide can be given in SSR-positive tumours or those with hormonal symptoms.
Other options include chemotherapy agents like Temozolamide, Capecitabine or platinum compounds.
Gastrointestinal NETs:
Complete resection of primary tumor along with metastatic lesions, can be done if possible.
Observation can be considered for asymptomatic patients with low-grade tumors following surgery.
For patients with symptoms or high tumor burden, Octreotide or Lanreotide is the treatment of choice.
Pancreatic NETs:
Complete resection of primary tumor along with metastatic lesions, can be done if possible.
Observation can be considered for asymptomatic patients with low-grade tumors following surgery.
For patients with symptoms or high tumor burden, Octreotide or Lanreotide is the treatment of choice.
For patients with progressive disease targeted therapy, agents like Everolimus or Sunitinib can be considered.
For SSR-positive tumors of all location progressing on Octreotide or Lanreotide, Peptide Receptor Radionuclide Therapy (PRRT) with 177Lu-dotatate is the recommended option.
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