95 Evaluating progression-free survival as a surrogate marker for overall survival in recurrent and advanced endometrial cancer, an EORTC young gynaecologic cancer group (EORTC-YGCG) study

Introduction/Background Progression-Free Survival (PFS) as a surrogate marker for Overall Survival (OS) has been a topic of debate. PFS poses challenges in capturing the true endpoint, as it only accounts for a limited period of the disease. To address this issue, we investigated the surrogacy of PFS for OS among recurrent/advanced endometrial cancer (EC) trials. Methodology We systematically reviewed randomized phase 2 and 3 clinical trials in advanced/recurrent EC, following PRISMA guidelines, with inclusion criteria based on mature PFS and OS data. We excluded trials reporting recurrence-free survival or disease-free survival. The primary endpoint was to assess overall surrogacy of PFS on OS outcomes among all trials. We estimated standardized treatment benefits using Wald statistics (z-scores) based on Hazard Ratios for OS and PFS. Exploratory analyses comprised cohorts with ≥50% or Results Out of 11,348 screened articles 238 were deemed for full-text screening and 11 were included in our final analysis. We detected a moderate correlation between PFS and OS (Spearman's rho = 0.69; p-value = 0.0022). Additionally, a Surrogate Threshold Effect (STE) with a z-score of 2.3 was identified, suggesting a low intersection point between the surrogate and the significant threshold for OS at α= 0.05. Sub-analyses revealed stronger correlations in trials with Conclusion PFS is an acceptable surrogate marker for OS to assess treatment efficacy in EC trials, showing a low STE to further predict a meaningful OS benefit. Disclosures Dr. Madariaga reports consultation fees from GSK, AstraZeneca and PharmaMar;participation in company sponsored speaker's bureau for GSK, AstraZeneca, Clovis and MSD. Dr. Herrera reports research supports from Accuray inc, Bioprotect, Bristol-Myers Squibb, Roche-ImFlame/ImCore, Nanobiotix, TherAGuIX, AstraZeneca, Eisai, MSD, SeagenProstate Cancer FoundationSan Salvatore FoundationBiltema Foundation; consultation fees from Johnson participation in a company sponsored speaker's bureau: Johnson consultation fees from AstraZeneca, Elli Lilly, GSK, MSD, Novartis. The rest of the authors have no COIs to report.