[Novel pharmacologic therapies in acromegaly]

Abstract

The primary aim of therapy should be to remove symptoms, reduce tumor bulk, prevent relapse, and improve long-term outcome. Surgery, radiotherapy and medical therapies are used to achieve these aims. Post-treatment mean "safe" serum growth hormone values of < 2.5 ng/ml should be the therapeutic goal. Transsphenoidal surgery remains the first line treatment for acromegaly. Patients with microadenoma can expect 85%, while those with macroadenoma 50% chance to achieve safe serum growth hormone levels. Less than 20% of acromegalics respond to treatment with bromocriptine, while quinagolide and cabergoline may show better clinical response; the success rate is higher for tumors secreting both growth hormone and prolactin. Dopamine agonists may be considered either in combination with somatostatin-analogues or as monotherapy in selected patients, and in those with co-secretion of prolactin. Octreotide (Sandostatin, Novartis) is a synthetic somatostatin-analogue, which is administered subcutaneously in doses between 100 and 250 micrograms 3 times daily. Long-acting octreotide (Sandostatin LAR, Novartis) contains octreotide incorporated into microspheres of biodegradable polymer. To effectively lower serum growth hormone levels, monthly injections of 10-30 mg of long-acting octreotide are needed, serum growth hormone falls to 2.5 ng/ml in 70% of cases, and serum insulin-like growth factor I normalizes in 67%. Slow release lanreotide (Somatuline SR, Ipsen) is an alternative depot long-acting somatostatin-analogue, which is administered in a dose of 30 mg intramuscularly every 14, 10 or 7 days. Both compounds are equally, if not more, effective than subcutaneous octreotide, and significantly improve patient compliance. Pegvisomant (Sensus Drug Development Corporation) is a genetically engineered growth hormone receptor antagonist, which inhibits growth hormone action. When given subcutaneously in a dose of 20 mg/day, serum insulin-like growth factor I levels return to normal in 90% of patients. Theoretical concerns of tumor expansion have not been a problem to date, but long term studies are needed. Primary medical--somatostatin-analogue--therapy is recommended if surgery fails, if the patient refuses or unsuited for surgery and it may be also considered in patients with macroadenoma with extra--but not suprasellar extension, since the surgical "cure" rates of these tumors are low.