Insulin-like growth factor (IGF) and IGF binding proteins in growth hormone dysregulation and abnormal glucose tolerance in small cell lung cancer patients

Growth hormone (GH) regulation, glucose tolerance and serum concentrations of insulin-like growth factor (IGF) and IGF binding proteins (IGFBP) have been investigated in small cell lung cancer (SCLC) patients. Elevated serum GH was observed in the patient and smoking control groups but not in non-smoking control subjects. Glucose suppression of GH was observed in the few SCLC patients with raised basal GH but most SCLC patients exhibited a paradoxical increase in GH following oral glucose. Abnormal glucose tolerance and insulin resistance with respect to plasma glucose was observed in most patients. Patients showing GH dysregulation exhibited higher serum concentrations of IGFBP-2 than those showing no increase in GH. Abnormal glucose tolerance was associated with decreased serum concentrations of IGF-I. Given reports of elevated IGFBP secretion in SCLC and inhibition of IGF-I bioactiviry by IGFBPs, these findings may indicate that increased serum IGFBPs disrupt IGF-I regulation of GH secretion and glucose homeostasis.