THE AROMATASE INHIBITOR LETROZOLE IN ADVANCED BREAST-CANCER - EFFECTSON SERUM-INSULIN LIKE GROWTH-FACTOR (IGF)-I AND IGF BINDING PROTEIN-3LEVELS

Serum insulin-like growth factor (IGF)-I and IGF-binding protein-3 lev els were measured in two groups of postmenopausal women with advanced breast cancer, who received the aromatase inhibitor letrozole 0.5 or 2 .5 mg p.o. once daily. Blood samples were obtained from 15 patients in each dose group at baseline, and one and three months after starting therapy. Circulating IGF-I and IGFBP-3 concentrations were determined by means of radioimmunoassay. In both dosage groups a statistically si gnificant increase in the IGF-I levels was observed during three month s of letrozole treatment (P = 0.003). In addition, the multiple testin g procedure yielded in the whole patient population a significant resu lt in the comparison between mean IGF-I values after three months of t herapy and those observed at baseline (P = 0.004), the estimated avera ge increase being of 24%. No significant result was obtained in the an alysis for the dose effect (P = 0.077) and for the time x dose interac tion (P = 0.208). Circulating IGFBP-3 levels did not appear to be affe cted by letrozole treatment in either of the dose groups. This is the first report concerning the short-term effects of letrozole on compone nts of the IGF system in breast cancer patients; further investigation s are warranted in order to confirm these preliminary data. (C) 1997 P ublished by Elsevier Science Ltd. All rights reserved.