Suppression of serum insulin-like growth factor-1 levels in breast cancer patients during adjuvant tamoxifen therapy.

Serial IGF-1 levels in patients prior to and during adjuvant tamoxifen (TAM) treatment were followed in a retrospective study. Serum IGF-1 levels were determined by radioimmunoassay in 19 patients taking TAM and 19 controls, matched for age, body weight and other treatments. IGF-1 levels at 2 years were significantly lower in TAM patients (P < or = 0.05) compared to control patients. We observed a significant mean drop from pretreatment to treatment IGF-1 levels by 19.9% in the TAM group (P < or = 0.005), but also noted a mean 11.4% decline in the control group (P < or = 0.025). A subgroup analysis suggested that premenopausal were relatively resistant to the IGF-1 lowering effects of TAM as compared to postmenopausal women.