Surrogate end points for overall survival in loco-regionally advanced nasopharyngeal carcinoma: An individual patient data meta-analysis

Background: Our objective was to evaluate progression-free survival (PFS) and distantmetastasis-free survival (DMFS) as surrogate end points for overall survival (OS) in randomized trials of chemotherapy in loco-regionally advanced nasopharyngeal carcinomas (NPCs). Methods: Individual patient data were obtained from 19 trials of the updated Meta-Analysis of Chemotherapy in Nasopharyngeal Carcinoma (MAC-NPC) plus one additional trial (total = 5144 patients). Surrogacy was evaluated at the individual level using a rank correlation coefficient q and at the trial level using a correlation coefficient R2 between treatment effects on the surrogate end point and OS. A sensitivity analysis was performed with two-year PFS/DMFS and fiveyear OS. Results: PFS was strongly correlated with OS at the individual level (q = 0.93, 95% confidence interval [CI] = 0.93 to 0.94) and at the trial level (R2 = 0.95, 95% CI=0.47 to 1.00). For DMFS, too, the individual-level correlation with OS was strong (q = 0.98, 95% CI=0.98 to 0.98); at trial level, the correlation was high but the regression adjusted for measurement error could not be computed (unadjusted R2 = 0.96, 95% CI=0.94 to 0.99). In the sensitivity analysis, two-year PFS was highly correlated with five-year OS at the individual level (q = 0.89, 95% CI=0.88 to 0.90) and at the trial level (R2 = 0.85, 95% CI=0.46 to 1.00); two-year DMFS was highly correlated with five-year OS at the individual level (q = 0.95, 95% CI=0.94 to 0.95) and at the trial level (R2 = 0.78, 95% CI=0.33 to 1.00). Conclusions: PFS and DMFS are valid surrogate end points for OS to assess treatment effect of chemotherapy in locoregionally advanced NPC, while PFS can be measured earlier.