Types of pituitary gland tumours

Tumours can affect the pituitary gland. A tumour is an abnormal growth of tissue formed when cells grow and divide more than they should. Almost all tumours of the pituitary gland do not spread to other parts of the body (metastasize), but they can grow into (invade) and destroy nearby areas such as bone, the brain, nerves that connect the eyes to the brain (optic nerves) and nasal sinuses.

A pituitary neuroendocrine tumour (PitNET) develops from the gland cells of the pituitary gland. It is the most common type of pituitary gland tumour. Most PitNETs start in the front part of the pituitary gland (anterior pituitary gland).

PitNETs have been called non-cancerous (benign) pituitary adenomas, but this term does not describe them very well. They can cause a lot of damage to nearby tissues and problems for people with these tumours. For this reason, the term pituitary adenoma is slowly being changed to PitNET.

PitNETs can be divided into groups based on the size of the tumour and how much it has grown into nearby areas (invasion). Sometimes doctors use a classification system to group the tumours into 4 grades (grades 1 to 4). The higher the grade number, the bigger the tumour and the more it has grown into nearby areas.

PitNETs are also classified as functioning or non-functioning.

Functioning tumours make too many hormones and cause symptoms. Most pituitary tumours are functioning tumours. They are named based on the type of hormone they make, including:

• prolactin-producing tumour (also called a prolactinoma) – the most common type of functioning tumour
• growth hormone–producing tumour
• adrenocorticotropic hormone (ACTH)–producing tumour
• thyroid-stimulating hormone (TSH)–producing tumour
• gonadotropin-producing tumour

Non-functioning tumours don’t make too many hormones. They are usually macrotumours and can cause symptoms by pressing on the pituitary gland and nearby tissues such as nerves.

Pituitary carcinoma is a cancerous (malignant) tumour of the pituitary gland that can spread to other parts of the body, such as the brain, spinal cord or outside of the skull. Pituitary carcinoma is very rare.

Most pituitary carcinomas are functioning tumours that make too many hormones.

It is not possible to tell the difference between pituitary carcinoma and a PitNET. So pituitary carcinoma is only diagnosed once it has spread to the central nervous system (CNS) or another part of the body.

Cancer can spread from where it started (primary site) to the pituitary gland. When this happens, it is called metastatic cancer, or secondary pituitary gland tumours. The most common types of cancer that spread to the pituitary gland are lung, breast and colon. Metastatic cancer in the pituitary gland is much more common than pituitary carcinoma.

Find out more about metastatic cancer.

The following pituitary gland tumours are uncommon:

• Rathke cleft cyst – a fluid-filled sac that forms between the front and back parts of the pituitary gland
• craniopharyngioma – a tumour near the pituitary gland that is made up of tissue that looks like the lining of the mouth
• gangliocytoma – a tumour made up of mature neurons
• pituicytoma – a tumour made of specialized glial cells( pituicytes) of the posterior pituitary gland