The Anti-Tumor Effects of the Fetal Estrogen Estetrol in Advanced Prostate Cancer

Background: Co-treatment of the fetal estrogen estetrol (E4) with androgen deprivation therapy (ADT) for advanced prostate cancer (PCa) may further inhibit endocrine PCa tumor stimulators including testosterone (T), prostate-specific antigen (PSA), follicle-stimulating hormone (FSH), and insulin-like growth factor-1 (IGF-1). Methods: A Phase II, double-blind, randomized, placebo-controlled study in advanced PCa patients requiring ADT (the PCombi study) was conducted to assess the effect of E4 co-treatment with LHRH agonist ADT on total T, free T, PSA, FSH, and IGF-1. Patients starting ADT were randomized 2:1 to 40 mg E4 (n=41) or placebo (n=21) for 24 weeks. Analyses were performed on the per-protocol population (PP), using the Wilcoxon-rank sum and the Kruskal-Wallis test. Results: The PP population consisted of 57 patients (37 ADT+E4; 20 ADT+placebo). All individual data of the four endocrine tumor stimulators are presented in figures in the paper and in supplementary tables, showing that E4 co-treatment almost completely suppressed FSH levels in all patients, on average by 98% versus 37% in the placebo group (p