An Overview of Phase 2 Clinical Trial Designs

Int J Radiat Oncol Biol Phys. 2022 Jan 1;112(1):22-29. doi: 10.1016/j.ijrobp.2021.07.1700. Epub 2021 Aug 4.


Clinical trials are studies to test new treatments in humans. Typically, these treatments are evaluated over several phases to assess their safety and efficacy. Phase 1 trials are designed to evaluate the safety and tolerability of a new treatment, typically with a small number of patients (eg, 20-80), generally spread across several dose levels. Phase 2 trials are designed to determine whether the new treatment has sufficiently promising efficacy to warrant further investigation in a large-scale randomized phase 3 trial, as well as to further assess safety. These studies usually involve a few hundred patients. This article provides an overview of some of the most commonly used phase 2 designs for clinical trials and emphasizes their critical elements and considerations. Key references to some of the most commonly used phase 2 designs are given to allow the reader to explore in more detail the critical aspects when planning a phase 2 trial. A comparison of 3 potential designs in the context of the NRG-HN002 trial is presented to complement the discussion about phase 2 trials.

Publication types

  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Clinical Trials, Phase II as Topic* / methods
  • Humans
  • Research Design*