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D. Jonker



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    OA 14 - New Paradigms in Clinical Trials (ID 681)

    • Event: WCLC 2017
    • Type: Oral
    • Track: Clinical Design, Statistics and Clinical Trials
    • Presentations: 1
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      OA 14.02 - Rethinking Progression-Free Survival (PFS) as a Clinical Trials Surrogate for Overall Survival (OS) (ID 10276)

      11:10 - 11:20  |  Author(s): D. Jonker

      • Abstract
      • Presentation
      • Slides

      Background:
      ►►OS assessment requires high follow-up times and patient numbers and is impacted by crossover (CO). OS hazard ratios (HRs) are generally inferior to PS HRs due to impact of post-progression survival (PPS) and CO. Some authors propose that absolute OS gains (ΔOS) should be similar to those in PFS (ΔPFS). Hence, ΔPFS might be a useful OS surrogate (Clin Cancer Res 2013;19:2646; Ann Oncol 2016;27:373).

      Method:
      To assess this further, we reviewed Journal of Clinical Oncology and New England Journal of Medicine 01/01/2012-06/12/2017 for randomized drug trials in incurable solid tumors. We extracted data for PFS and OS medians and HRs, calculated ΔPFS and ΔOS (experimental medians minus control medians), and did paired comparisons between 2-6 different arms in each study (245 comparisons across 201 trials).

      Result:
      Mean ΔOS across studies (1.03 months) was similar to mean ΔPFS (1.06 months) (n=201 evaluable, p=0.88). ΔOS correlated with ΔPFS (r=0.50, p<0.0001). With CO in <20% of patients or unstated %CO (n=144), mean ΔOS and ΔPFS were 0.93 and 0.92 months, respectively. With CO in >20% of patients (n=57), mean ΔOS and ΔPFS were 1.29 and 1.41 months, while with CO>50% (n=20), they were 1.4 and 1.9 months. OS HRs (mean=0.92) were inferior to PFS HRs (mean=0.82, n=196, p<0.0001), although OS and PFS HRs correlated with each other (r=0.64, p<0.0001). With CO<20% or unstated (n=135), mean OS and PFS HRs were 0.93 and 0.83, while with CO>20% (n=61), they were 0.90 and 0.80, and with CO>50% (n=20), they were 0.94 and 0.71.

      Conclusion:
      OS HRs were inferior to PFS HRs, probably due to PPS, competing causes of death and CO. The better mean gains and HRs in high vs low CO trials may be due to more frequently allowing CO in trials with more effective therapies. This increases risk of false-negative OS results with effective therapies if CO is permitted, but it is potentially unethical to withhold CO of effective therapies. With PFS, clinically insignificant gains may be statistically significant. Since ΔOS and ΔPFS are similar, an alternate approach would be a primary study outcome requiring PFS HR to be statistically significant and ΔPFS 95% CIs in a range considered clinically relevant for OS gains. To better understand the limitations of this approach, we are analyzing examples with minimal OS gains despite ΔPFS>2 months and examples of ΔOS>2 months but no gain in PFS, and have formulated a potential biological/statistical explanation for the latter.

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