Forsythe A, et al. - In this formal investigation of the surrogacy of progression-free survival (PFS) or time to progression (TTP) for overall survival (OS) in hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) metastatic breast cancer (MBC), researchers analyzed randomized controlled trials (RCTs) that reported both median PFS/TTP and OS. They used an exploratory analysis to determine the influence of three covariates (chemotherapy vs hormonal/targeted therapy, PFS vs TTP, and first-line therapy vs second-line therapy or greater) on OS prediction. A significant link was found between PFS/TTP and OS, which may justify the use of PFS/TTP as a surrogate for OS benefit in HR+, HER2– MBC. For chemotherapy and hormonal/targeted therapy, these outcomes proved consistent.