Alternative names for somatostatinoma

Functional pancreatic neuroendocrine tumour

What are somatostatinomas?

Somatostatinomas are part of a group of rare neuroendocrine tumours and may be referred to as functional pancreatic neuroendocrine tumours. These tumours arise from neoplastic cells in the pancreas and duodenum. These cancerous cells produce large (abnormal) amounts of the hormone somatostatin.

Somatostatin is a hormone normally produced by D-cells within the endocrine pancreas (islets of Langerhans) and other parts in the gastrointestinal tract. It inhibits the release of gastrointestinal hormones such as insulin, glucagon,  gastrin, secretin and cholecystokinin, which causes  reduced gastrointestinal motility and gastric secretions as well as suppression of pancreas secretions and gall bladder contraction. Besides its production and function within the digestive tract, somatostatin is also produced by neurons in the hypothalamus, where it reduces growth hormone signalling. All these inhibitory actions of somatostatin are thought to be responsible for the clinical presentation of the tumour. Patients with a somatostatinoma are susceptible to developing insulin resistance and diabetes mellitus, and gallstones (due to reduced gall bladder contraction). In addition, they may experience loose fatty stools (due to reduced secretion of enzymes involved in the digestion of fatty food) and weight loss.

What causes somatostatinomas?

Somatostatinomas are extremely rare tumours affecting about 1 person in every 40 million. The direct causes of somatostatinomas are currently unknown. Females and males are similarly affected with most patients in their forties to sixties. About 1 in 10 patients may develop somatostatinomas due to an underlying genetic condition such as multiple endocrine neoplasia type 1 (MEN1), neurofibromatosis type 1, von Hippel-Lindau disease or tuberous sclerosis.

What are the signs and symptoms of somatostatinomas?

The inhibitory effects of somatostatin on other endocrine and exocrine tissues account for the symptoms of this tumour. There are two distinct types of symptom presentations depending upon the location of the tumour.

1. Somatostatinomas that arise from the pancreas are associated with glucose intolerance (GI), a condition where cells are unable to uptake glucose from the bloodstream due to the lack of insulin (suppressed by too much somatostatin). Glucose intolerance precedes diabetes mellitus type 2, which is characterised by the complete absence of insulin. Other symptoms including abdominal pain/nausea due to gallstones; fatty/loose stools; and reduced acid production in the stomach are caused by somatostatins’ inhibitory effect on digestive and GI hormones.
2. The tumours that arise from the duodenum mostly lead to symptoms due to mechanical obstruction of the small intestine such as abdominal pain/discomfort; nausea; and vomiting.

If the tumour has spread to the liver or adjacent lymph nodes (metastasis); patients may present jaundice, by which the skin, the whites of the eyes and the mucous membranes turn yellow because of high levels of bilirubin, a yellow-orange bile pigment (produced in the liver). Another significant sign of an advanced tumour stage is weight loss.

Are somatostatinomas inherited?

Most of the somatostatinomas are sporadic; although they may run in families as part of associated genetic disorders like multiple endocrine neoplasia type 1 syndrome or neurofibromatosis type 1.  

How are somatostatinomas diagnosed?

In patients suspected to have somatostatinoma, initial blood tests may show elevated somatostatin hormone levels (usually levels increase 1000-fold or higher).

Different imaging studies allow the direct localization of the tumour and the assessment of metastasis in other tissues/lymph nodes. Common radiological imaging studies are computerised tomography (CT) scans or endoscopy, which is usually carried out for the investigation of unexplained abdominal pain, weight loss or diarrhoea. Endoscopy involves inserting a long flexible tube with a camera attached to the end, through the patient's throat, for example. It is used to collect images of the inside of your body.

A CT scan of the abdomen is used to look for primary tumours in the pancreas or duodenum as well as assessing any spread of the disease locally (lymph nodes) or distant spread to the liver.

Magnetic resonance imaging (MRI) is another imaging technique. It is stated that this method might be more precise than CT, in particular when evaluating small primary and metastatic tumour nodules within the pancreas or liver.

Somatostatin receptor scintigraphy (octreoscan) is a specialised investigation available only in a limited number of centres and is a novel nuclear medicine imaging technique. A radiolabelled somatostatin analogue is administered to the patients. The labelling allows the detection and visualisation of tumour tissues. It is helpful in diagnosing the localisation of the tumour and assessing tumour spread.

The diagnosis of somatostatinoma can only be confirmed if a tissue sample from a suspected patient with this condition is obtained (on biopsy or post-surgery), marked with special stains and assessed under the microscope (histology).

How are somatostatinomas treated?

Exact treatment will vary between patients and are tailored to their individual needs. The definitive treatment for a somatostatinoma is surgical removal of the tumour, wherever possible. However, in most patients the tumour will have spread to the liver making surgical removal of the tumour more difficult. In cases where the tumour has spread to the liver (called liver metastasis), a segment of liver may be removed surgically. If surgery is not possible, another option is hepatic embolization or chemo-embolisation where a chemical/blood clot is introduced to the liver’s artery supplying blood to the area of the tumour, which will cause that part of the tissue to die.

Medical treatment of somatostatinoma includes chemotherapy. It is also important to implement supportive medications like antidiabetic agents and pancreatic extracts/enzymes in order to improve glucose handling and to reduce diarrhoea and malabsorption, respectively.

In addition, somatostatinoma patients may benefit from nutritional therapies to adjust fluid, electrolyte and nutritional deficits.

Are there any side-effects to the treatment?

Surgical treatment is associated with general risks common to all types of surgery such as bleeding and infection.

Chemotherapy is associated with side-effects such as reduced immunity to infections, nausea, vomiting and alopecia (hair loss). Patients should discuss any concerns with their doctor or specialist.

What are the longer-term implications of somatostatinomas?

The long-term prognosis of somatostatinoma depends on whether or not the cancer has spread to the liver and adjacent lymph nodes. Patients may need to take long-term medication to control associated conditions such as diabetes mellitus. If the tumour is caught early before spreading to the liver and can be removed by surgery, patients have a much improved prognosis. Eating a balanced diet and having a healthy lifestyle can also help in the management of somatostatinoma.