Insulinoma: symptoms, tests and treatment of this rare pancreatic tumour

Cancer Research UK describes insulinomas as rare neuroendocrine tumours (NETs) that start in the insulin-making cells of the pancreas, called islet cells, which is why they are also called islet cell tumours. They are a type of functioning NET, meaning they make and release abnormal levels of a hormone, in this case insulin.

Insulin controls the amount of glucose in the blood by helping it move into cells. When a tumour makes too much, blood sugar falls too low. The charity notes that many people think of diabetes when they hear about insulin, but in insulinoma the body makes too much insulin, which causes low blood sugar, whereas in diabetes blood sugar is too high.

Symptoms are caused by changes in blood sugar, and usually occur when blood sugar is low. Cancer Research UK lists weakness and tiredness, headaches, problems with the eyes, forgetfulness and confusion, behaving in a way that is not normal for you, hunger and sickness, sweating and tremors, and palpitations. Low blood sugar can be dangerous if you do not eat something straight away, and may cause fits and unconsciousness.

Doctors use Whipple’s triad to help diagnose it: symptoms of low blood sugar such as dizziness and sweating, a blood sugar level lower than 2.2 mmol per litre, and feeling better after eating sugary food or having a glucose drip.

The charity advises seeing a doctor if you have symptoms that are unusual for you, or that will not go away or are getting worse, while noting that symptoms are unlikely to be cancer.

Because insulinomas are rare, a GP may arrange tests for other, more common causes of low blood sugar first. A GP may refer you to an endocrinologist, and if an insulinoma is found you are referred to a neuroendocrine cancer team.

Tests can include checking blood sugar, a fasting test, CT and MRI scans, an endoscopic ultrasound to look at the stomach, pancreas and bile ducts and take biopsies, and specialised radioactive scans such as PET. In the fasting test you stay in hospital with regular blood tests to see if blood sugar falls when you do not eat, and you can drink water but not eat for up to 72 hours.

Pathologists assess grade (1 to 3, from slow- to fast-growing) and doctors determine stage (1 to 4). Risk factors include inherited conditions such as multiple endocrine neoplasia 1 (MEN1) and Von Hippel-Lindau disease, and a family history of cancer.

Treatment is planned by a multidisciplinary team and depends on the tumour’s location and size, how many tumours there are, whether it has spread, your general health and your symptoms. A clinical nurse specialist is often the main contact.

Surgery to remove the insulinoma is usually the main treatment. It can be open or keyhole, and options include enucleation, where only the tumour is removed, a distal pancreatectomy, a pylorus-preserving pancreaticoduodenectomy or a Whipple’s operation. If the tumour has spread to the liver, liver tumours may be removed at the same time. In people with MEN1 or Von Hippel-Lindau syndrome, the surgeon may suggest removing the whole pancreas because more tumours are likely to develop.

If surgery is not possible, radiofrequency ablation uses heat to destroy the cancer when someone is too unwell for surgery and the insulinoma is only in the pancreas, and other treatments are used if the tumour has spread or returned.

Cancer Research UK says that symptoms of insulinoma can be difficult to cope with, and it helps to be aware of the symptoms of low blood sugar, which include headaches, double or blurred vision, confusion and dizziness, tiredness, sweating and constantly feeling hungry. Your doctor or dietitian can tell you which foods to eat to keep blood sugar level and prevent it going too low.

Surgery for insulinoma includes major operations with risks, and the team will talk through benefits and risks before you decide. Because insulinomas are rare, care is usually concentrated in neuroendocrine cancer teams that meet as a multidisciplinary group, and your clinical nurse specialist is often the main point of contact throughout.