Long-term effects of fenretinide, a retinoic acid derivative, on the insulin-like growth factor system in women with early breast cancer

High insulin-like growth factor-I (IGF-I) levels are associated with an inc reased risk of breast cancer in premenopausal women. Because the synthetic retinoid fenretinide showed a beneficial effect on second breast cancers in premenopausal women in a Phase III trial, we studied its long-term effects on IGF-I levels. We measured, at yearly intervals for up to 5 years, the c irculating levels of IGF-I, IGF binding protein (BP)-3, and their molar rat io in 60 subjects less than or equal to 50 years of age and 60 subjects > 5 0 years of age allocated either to fenretinide or no treatment. In women le ss than or equal to 50 years of age, measurements of IGF-H, IGFBP-1, and IG FBP-2 were also performed. The associations between biomarkers and drug or metabolite plasma concentrations were also investigated. All biomarkers wer e relatively stable over 5 years in the control group. Compared with contro ls and after adjustment for baseline, treatment with fenretinide for 1 year induced the following changes: IGF-I, -13% [95% confidence interval (CI), -25 to 1%] in women less than or equal to 50 years of age and -3% (95% CI, -16 to 13%) in women >50 years of age; IGFBP-3, -4% (95% CI, -12 to 6%) in both age groups; IGF-I:IGFBP-3 molar ratio, -11% (95% CI, -22 to 1%) in wom en less than or equal to 50 years of age and 1% (95% CI, -11 to 16%) in wom en > 50 years of age. These effects were apparently maintained for up to 5 years, although fewer samples were available as time progressed. No change in other IGF components was observed. Drug and metabolite concentrations we re negatively correlated with IGF-I and IGF-I:IGFBP-3 molar ratio in women less than or equal to 50 years of age. Fenretinide induces a moderate decli ne of IGF-I levels in women less than or equal to 50 years of age. The asso ciation between IGF-I change and the reduction of second breast cancers in premenopausal women warrants further study.