Abstract P1-16-07: Progression-free survival is a surrogate of survival in maintenance therapy for metastatic breast cancer: Randomized trial level analysis

Abstract

Abstract Background:The validity of progression-free survival (PFS) as a surrogate end point for overall survival (OS) in maintenance therapy trials of metastatic breast cancer (MBC) is uncertain. We aimed to compare treatment effect sizes and the strength of associations between OS and PFS in trials of maintenance therapy for MBC. Methods: We searched for randomized trials investigating maintenance chemotherapy, endocrine therapy or immunotherapy after first-line chemotherapy in MBC and selected those reporting results for both OS and PFS. Treatment effect size differences between OS and PFS by a ratio of hazard ratios (rHRs) with 95% confidence intervals [CIs] were evaluated using random effects analysis. Surrogacy were analyzed using a weighted linear regression model, correlations were evaluated by squared correlation R2. Results: We analyzed data from 16 trials and 3,898 patients that received maintenance chemotherapy, endocrine therapy or immunotherapy for MBC. In the all trial-level analysis, treatment effect sizes were 28% greater for PFS than for OS (combined rHR, 0.72; 95% CI, 0.62 to 0.85, P < 0.001), and the correlation coefficient R2 between PFS and OS was 18% (95% CI, 12% to 26%). Differences were greater with PFS than OS for trials of maintenance chemotherapy compared with observation (rHR, 0.72; 95% CI, 0.59 to 0.80, P < 0.001), and the correlation coefficient R2between treatment effects on PFS and on OS ranged from 12% (95% CI, 8% to 16%) when all trials were considered to 40% (95%CI, 30% to 54%) after exclusion of one highly influential trial by sensitivity analysis. Differences were also great for trials of maintenance endocrine therapy vs. observation (rHR, 0.54; 95% CI, 0.44 to 0.66), and immunotherapy vs. observation (rHR, 0.85; 95% CI, 0.80 to 0.91). Conclusion: PFS was greater than OS in the treatment effect sizes, which is a valid surrogate end point for OS to assess treatment effect in MBC maintenance therapy trials. PROSPERO registry: No. CRD42017071858; Support: ChiCTR-IIR-17014036, SYS-C-201801. Citation Format: Song E, Yao H, Yu Y, Ou Q, Wang Y. Progression-free survival is a surrogate of survival in maintenance therapy for metastatic breast cancer: Randomized trial level analysis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-16-07.