Surrogate threshold effect based on a meta-analysis for the predictive value of progression-free survival for overall survival in hormone receptor-positive, HER2-negative metastatic breast cancer

PURPOSE: Clinical trials investigating therapies for metastatic breast cancer (mBC) generally use progression-free survival (PFS) as primary endpoint, which is not accepted as patient-relevant outcome within the German benefit assessment. Hence a validation of PFS as surrogate endpoint for overall survival (OS) is needed, e.g., in the indication of HR+, HER2-negative mBC. METHODS: A systematic search was conducted. RCT were included if at least one study arm investigated fulvestrant, letrozole, tamoxifen, exemestane, or anastrozole. Additionally, hazard ratios reported for OS/PFS including confidence interval or standard error were mandatory. Pearson correlation coefficient was calculated to estimate the relation of surrogate endpoint PFS and patient-relevant outcome OS as well as the surrogate threshold effect (STE) which is used to determine thresholds for the estimate of the surrogate endpoint. RESULTS: 16 studies with 5324 patients in total were included in the analyses. The correlation between hazard ratios of PFS and OS was statistically significant (r = 0.72, 95% CI 0.35–0.90) representing a positive linear relationship. STE analysis was applied. The meta-regression model revealed a STE for HR(PFS) of 0.60 and sensitivity analyses underlined robustness of the results. CONCLUSIONS: Based on the derived STE, it is possible to draw conclusions on a significant effect in OS for a hypothetical trial demonstrating an upper confidence limit of HR(PFS) < 0.60 in PFS. However, only final OS results are able to confirm if a clinical relevant difference in survival time can be achieved. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10549-019-05262-4) contains supplementary material, which is available to authorized users.