Progression-free survival as surrogate endpoint of overall survival in esophageal squamous cell carcinoma: a real-world data and literature-based analysis

BACKGROUND: The surrogacy of progression-free survival (PFS) for overall survival (OS) in esophageal squamous cell carcinoma (ESCC) remains unelucidated. This study aimed to determine the validity of PFS as a surrogate endpoint for OS in ESCC patients treated with definitive radiotherapy or definitive chemoradiotherapy (dRT/dCRT), as well as characterize the prognostic factors and survival of such patients. METHODS: A total of 3662 patients from 10 cancer centers were enrolled. One-, 2-, and 3-year PFS (PFS12, PFS24, and PSF36, respectively) were used as time points for analysis. At each time point, ESCC-specific mortality and OS were characterized using competing risk and conditional survival models, while correlation between PFS and OS was evaluated by linear regression. RESULTS: At PFS12, PFS24, and PFS36, a progressive decrease in 5-year ESCC-specific mortality (35.2%–13.4%) and increase in 5-year OS (46.6%–62.9%) were observed. Regardless, the OS of patients remained markedly lower than those of the age- and sex-matched Chinese general population. TNM stage remained a significant prognostic factor at PFS36. Strong correlation was found between 3-year PFS and 5-year OS, which was further externally validated. CONCLUSIONS: Three-year PFS may act as a potential surrogate endpoint for 5-year OS. TNM stage was considered a significant prognostic factor for OS, and may represent the optimal prognostic tool to guide clinical decision-making and post-treatment follow-up.