Due to lack of hormone overproduction in non-functioning pituitary adenomas (NFPAs), only the symptomatic adenomas or large adenomas with proven growth and risk for symptoms in near future will undergo pituitary surgery. The remaining adenomas are monitored regularly. Operation of these large adenomas will rarely remove all tumour tissue, and there is also a risk of worsening of pituitary function. Often, adenomas with the highest growth potential are operated several times and some also need radiation therapy, providing additional risk for pituitary failure. Unlike some of the hormone-producing adenomas, there is no established pharmacological treatment for NFPAs. However, there are a few non-randomized studies suggesting that treatment with dopamine agonists may slow growth, and also induce tumour shrinkage. At present, cabergoline is the dopamine agonist most widely used in the treatment of pituitary adenomas secreting prolactin.

Aim is to study the effect of medical treatment with cabergoline in non-functioning pituitary adenomas on the change in tumour volume.

Inclusion Criteria:

• A previously untreated non-functioning pituitary macroadenoma (largest diameter ≥ 10 mm) with either demonstrated growth on repeated MRI scans or ≤ 2 mm distance to chiasma opticum, or:
• a residual non-functioning pituitary adenoma after surgery (largest diameter ≥ 5 mm) that is either extrasellar and/or with documented growth after surgical treatment of a non-functioning pituitary macroadenoma

Exclusion Criteria:

• Clear indication for surgery at the time of inclusion
• Previous radiation therapy
• Pituitary surgery the last 6 months
• Previous apoplexy/bleeding in the adenoma
• Pregnancy or lactation
• Contraindications for cabergoline treatment (Known cardiac valvular disease, known pulmonal, pericardial or retroperitoneal fibrosis, clinical significant liver insufficiency, use of medications that interact with cabergoline
• unfit to participate due to any other reason