Pegvisomant Treatment in Gigantism Caused by a Growth Hormone-secreting Giant Pituitary Adenoma

BACKGROUND: Gigantism is rare with the majority of cases caused by a growth hormone (GH)-secreting pituitary adenoma. Treatment options for GH-secreting pituitary adenomas have been widened with the availability of long-acting dopamine agonists, depot preparations of somatostatin analogues, and recently the GH receptor antagonist pegvisomant. CASE REPORT: A 23-year-old male patient presented with continuous increase in height during the past 6 years due to a GH-secreting giant pituitary adenoma. Because of major intracranial extension and failure of octreotide treatment to shrink the tumour, the tumour was partially resected by a trans-frontal surgical approach. At immunohistochemistry, the tumour showed a marked expression of GH and a sparsely focal expression of prolactin. Somatostatin receptors (sst) 1-5 were not detected. Tumour tissue weakly expressed dopamine receptor type 2. The Gs alpha subunit was intact. Conversion from somatostatin analogue to pegvisomant normalized insulin-like-growth-factor-I (IGF-I) levels and markedly improved glucose tolerance. CONCLUSION: Pegvisomant is a potent treatment option in patients with pituitary gigantism. In patients who do not respond to somatostatin analogues, knowledge of the SST receptor status may shorten the time to initiation of pegvisomant treatment.