First line treatment is the removal of a pituitary tumour. This procedure is performed by a neurosurgeon. The best outcomes are achieved by neurosurgeons with experience in removing pituitary tumours. These surgeons are often affiliated with Pituitary Centres of Excellence.
Medical therapy can be used if the surgeon is unable to remove all, or enough of the pituitary tumour to decrease the growth hormone (GH) production and bring the IGF-1 into normal range. In some circumstances, the patient may be unable or unwilling to undergo surgery making medical therapy a first option.
Although clinical research continues to investigate and develop new therapies, currently 3 classes of therapy are used. These therapies target specific locations in the pathway from growth hormone production to its action on body cells.
- The 1st class of drugs most frequently used are somatostatins.
The hypothalamus and other locations (such as the pancreas and GI tract) produce somatostatin, also know as growth hormone inhibiting hormone and somatotropin releasing-inhibiting hormone.
Drugs that simulate, or increase somatostatin stop the production of GH. These drugs are known as somatostatin analogues or somatostatin receptor agonists.
The first drugs in this class were called first generation somatostatin analogues or ligands (SRLs) and included Octreotide and Lanreotide. Pasireotide was developed later as a second generation SRL. Long acting (LAR) formulations are administered every 30 days by injection and allow for extending the interval between doses in well controlled patients. However, only about 30-40% of patients are controlled on any one drug.
Oral Octreotide is approved for use in some countries as a twice daily capsule. This drug requires fasting prior to and after administration to allow absorption
- The 2nd class of drugs are GH receptor blockers or antagonists. All body organs, tissues, muscles, bones etc, have GH receptors on their cell surfaces that attract GH and guide it into the cell for growth and repair. GHR blockers bind to the receptor and stop GH from binding thereby preventing its action. Pegvisomant is currently the only drug in this class and controls GH levels in around 70% of patients but is given in a daily, under the skin injection.
- The 3rd class, dopamine agonists (DA) ,can weakly inhibit GH production the pituitary. DA such cabergoline may be used as an additional therapy in some patients.
- Therapies may be delivered as a single drug (monotherapy) or as a combination of drugs to improve the control of GH secretion.
If surgery and/or medical therapy fail to control GH excess, radiation therapy may be recommended.
Several types of radiation therapy are used according to characteristics of the tumour. This treatment is usually managed by a radiation oncologist:
- Fractionated radiation therapy. This is delivered in small doses of radiation over several weeks
- Stereotactic radiosurgery (SRS)/stereotactic radiation therapy (SRT). This is usually delivered in one therapy session.