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Sample size adjustment designs with time-to-event outcomes: A caution.

Boris Freidlin1, Edward L Korn1

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Summary

Sample size adjustment designs in time-to-event trials may inflate treatment effects and recommend ineffective therapies. These designs offer no efficiency advantage over group sequential methods and are therefore unjustified.

Keywords:
Adaptive designconditional powergroup sequential designinterim analysispromising zonesample size re-estimation

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Area of Science:

  • Biostatistics
  • Clinical Trials
  • Survival Analysis

Background:

  • Sample size adjustment designs allow increasing sample size based on interim analysis in randomized clinical trials.
  • While group sequential designs are efficient, sample size adjustment offers flexibility by incorporating external information.
  • The CDL design limits adjustments to promising interim results in time-to-event settings.

Purpose of the Study:

  • To investigate the performance of sample size adjustment designs in time-to-event trials using the CDL approach.
  • To evaluate how interim outcome data influences trial results and decision-making.

Main Methods:

  • Utilized the CDL sample size adjustment design for time-to-event trials.
  • Employed simulations to assess design performance under varying treatment effect magnitudes.
  • Examined two strategies for increasing events: extending follow-up or enrolling additional patients.

Main Results:

  • Interim data can enrich final analysis with events from periods of strongest treatment effect, potentially inflating the observed effect.
  • Sample size adjustment designs can increase the probability of recommending ineffective therapies in "clinical null" scenarios.
  • The CDL design offers little gain in unconditional power compared to fixed-sample-size designs.

Conclusions:

  • Interim access to survival curve data may compromise trial integrity.
  • Sample size adjustment designs lack efficiency advantages over group sequential designs.
  • The use of sample size adjustment designs in time-to-event settings is not justified.