IGF1 and acromegaly: Butz and colleagues emphasized that while IGF-1 levels are the key factor in the diagnosis and monitoring of acromegaly, GH measurements should not be ignored, as these two hormones reflect different aspects of the disease: GH is a measure of the secretory activity of the tumor and provides a correlate of pituitary GH secretion, while IGF-1 is a measure of biochemical and biological activity of the disease and the peripheral response to circulating GH [33,34].