IGF-1 axis changes with ADT and docetaxel in metastatic prostate cancer

Androgen deprivation therapy (ADT) forms the cornerstone of treatment in locally advanced and metastatic prostate cancer (PCa). Since the growth hormone-insulin-like growth factor (GH-IGF-1) axis has been implicated in prostate tumorigenesis, we aimed to evaluate the association between IGF-1 and its binding proteins on outcomes in men with metastatic PCa treated with ADT, with or without docetaxel (D). We analyzed serum samples for IGF-1 and its family proteins from baseline, 6 months post-randomization, and at the time of progression in men enrolled to receive ADT +/- D in the phase 3 CHAARTED trial. The key outcomes were time to the development of castrate-resistant prostate cancer and overall survival (OS). About 560 patients had samples available for analysis. At 6 months, significant increases in IGF-BP1 (mean Delta+27.4%, P = 0.033), IGF-BP3 (mean Delta+10.3%, P < 0.001), and IGF-BP4 (mean Delta+31.1%, P < 0.001) were seen in the ADT + D group, while the ADT group showed an increase in IGF-BP3 (mean Delta+5.5%, P = 0.015). A higher IGF-1:IGF-BP1 ratio at baseline and after 6 months was associated with improved OS in both the ADT (baseline: hazard ratio (HR) = 0.77, P = 0.026; 6 months: HR = 0.83, P = 0.036) and ADT + D groups (baseline: HR = 0.78, P = 0.04; 6 months: HR = 0.81, P = 0.018). Patients with a log10IGF-1:IGF-BP1 ratio >1.3 at baseline had improved OS when meta-analyzed with data from a prior cohort (HR = 0.71). A higher baseline and 6-month IGF-1:IGF-BP1 ratio was associated with better OS. Further exploration of the IGF-1 axis will be important to assess its role as a predictive biomarker and to target this axis in therapeutic trials.