The majority of tumours in MEN I are slow growing and benign (non-cancerous). They can affect:
- Parathyroid gland - controls calcium in the blood, bones and urine. Hyperparathyroidism (over-activity of the parathyroid gland) is associated with high levels of calcium in the blood (hypercalcaemia). This can cause tiredness, weakness, muscle or bone pain, indigestion, kidney stones or thinning of the bones, poor memory, irritability, ulcers and bone fractures.
- Pancreatic islet cells - release hormones that help with digestion and metabolism of nutrients, such as glucose. Tumours in the pancreatic islet cells are associated with the release of excessive amounts of hormones such as gastrin or insulin. Over-secretion of gastrin is associated with formation of severe ulcers in the stomach and small intestine which may cause severe vomiting with blood and/or diarrhoea. If left untreated, these may cause rupture of the stomach or intestine. Over secretion of insulin is associated with a low blood glucose that can cause feeling hungry and sweaty, and if severe then unconsciousness and fits.
- Pituitary gland - plays a critical role in regulating growth and development, metabolism and reproduction. It releases prolactin, growth hormone and other key hormones. Symptoms associated with tumours in the pituitary gland include a loss or irregularity of the menstrual cycle, headaches, high blood pressure and eye problems.
- Adrenal gland - plays a critical role in regulating salt and water balance, and in combatting stress. It releases steroids and catecholamines (such as adrenaline). The tumours usually do not release hormones and when they do, these are usually steroids, whose excess results in weight gain and symptoms associated with high blood pressure and diabetes.