The challenges of reliance on insulin-like growth factor I in monitoring disease activity in patients with acromegaly.

ABSTRACT

Serum insulin-like growth factor I (IGF-I) is an important marker of disease activity in patients with acromegaly, and epidemiological data indicate control of circulating IGF-I in patients with acromegaly restores life expectancy to normal. Improvements in the quality of, and access to, IGF-I assays has encouraged monitoring of acromegaly with IGF-I, although circulating growth hormone (GH) and IGF-I values provide different information, so ideally both should be monitored. However, the introduction of the GH receptor antagonist pegvisomant poses new challenges. Pegvisomant binds with high affinity to GH receptors, thereby blocking the action of GH at the tissue level and rendering the hormone biologically inactive. This leaves IGF-I as the principal marker of disease activity. It is conceptually possible to induce a state of functional GH deficiency (GHD) with pegvisomant with IGF-I values within the normal range. With the goal of minimizing the risk of over-treatment and GHD, we have provided preliminary guidance on the target range for IGF-I in patients receiving pegvisomant based on the gender- and decade-based percentile ranges for IGF-I of adult patients with untreated GHD enrolled in the Pfizer International Metabolic Database (KIMS).