Zhao S, et al. - In this study including 50 trials with 22,804 patients, the substitution of progression-free survival (PFS) and milestone survival for overall survival (OS) was assessed in second-line non-small cell lung cancer (NSCLC) trials investigating chemotherapy, targeted therapy, and immunotherapy, respectively. On the basis of pre-analysis, the milestone time point was set at one-year. Using a two-stage meta-analytic validation model, researchers evaluated the links between surrogate endpoint (SE) and OS and associations between treatment effects on SE and OS. They expressed treatment effects on SE and OS as PFS hazard ratios (HR_PFS), 1 yr-milestone ratio (Ratio_1y-SUR) and HR_OS. They also carried out subgroup analyses stratified by treatment types and trial publication years in order to assess the surrogacy in different clinical contexts. Findings highlighted a strong correlation of one-year survival with OS. They did not find any link between PFS and OS. In immunotherapy trials, a strong HR_PFS-HR_OS correlation was observed which suggests the potential of PFS as a SE in NSCLC trials involving immunotherapies.