Original Articles
Multitrial Evaluation of Progression-Free Survival as a Surrogate End Point for Overall Survival in First-Line Extensive-Stage Small-Cell Lung Cancer

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Introduction:

We previously reported that progression-free survival (PFS) may be a candidate surrogate end point for overall survival (OS) in first-line extensive-stage small-cell lung cancer (ES-SCLC) using data from three randomized trials (Foster, Cancer 2011). In this validation study (N0424-Alliance), we assessed the patient-level and trial-level surrogacy of PFS using data from seven new first-line phase II/III ES-SCLC trials and across all 10 trials as well (seven new, three previous).

Methods:

Individual patient data were utilized across the seven new trials (2259 patients) and all 10 trials (2855 patients). Patient-level surrogacy (Kendall’s τ) was assessed using the Clayton copula bivariate survival model. Trial-level surrogacy was assessed through association of the log hazard ratios on OS and PFS across trials, including weighted (by trial size) least squares regression (WLS R2) of Cox model effects and correlation of the copula effects (copula R2). The minimum effect on the surrogate (MES) needed to detect a nonzero treatment effect on OS was also calculated.

Results:

The median OS and PFS across all 10 trials were 9.8 and 5.9 months, respectively. PFS showed strong surrogacy within the 7 new trials (copula R2 = 0.90 [standard error = 0.27], WLS R2 = 0.83 [95% confidence interval: 0.43, 0.95]; MES = 0.67, and Kendall’s τ = 0.58) and across all 10 trials (copula R2 = 0.81 [standard errors = 0.25], WLS R2 = 0.77 [95% confidence interval: 0.47–0.91], MES = 0.70, and Kendall’s τ = 0.57).

Conclusions:

PFS demonstrated strong surrogacy for OS in first-line ES-SCLC based on this external validation study of individual patient data. PFS is a good alternative end point to OS and should be considered when resource constraints (time or patient) might make it useful or desirable in place of OS. Additional analyses are needed to assess its appropriateness for targeted agents in this disease setting.

Key Words

Extensive-stage small-cell lung cancer
Surrogate endpoints
Pooled analysis
Progression-free survival
Overall survival

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This study was supported, in part, by grants from the National Cancer Institute to the North Central Cancer Treatment Group (CA25224) and to the Alliance for Clinical Trials in Oncology (Monica M. Bertagnolli, MD, Chair, CA31946) and to the Alliance Statistics and Data Center (Daniel J. Sargent, PhD, CA33601). NCIC Clinical Trials Group is supported by funding received from the Canadian Cancer Society Research Institute (Grants #021039 and #015469) and the JCOG trial was supported by the Grant of Ministry of Health, Labour and Welfare in Japan. The content is solely the responsibility of the authors and does not necessarily represent the views of the National Cancer Institute, the National Institute of Health, or the other groups (JCOG, Canadian Cancer Society Research Institute).

Disclosure: Nathan R. Foster, MS, Lindsay A. Renfro PhD, Sumithra J. Mandrekar, PhD, and Keyue Ding, PhD received NCI or NIH grant support for the submitted work, Xiaofei F. Wang, PhD received Duke University and NIH funding for the submitted work, Suresh S. Ramalingam, MD received consultancy money from the following companies: Abbrie, Amgen, Celgene, AstraZeneca, Ariad, Areo, Lilly, Genentech, Novartis, and BMS. For the remaining authors, none were declared.