Single-arm phase 3 designs: An oxymoron?

Background: Since the 1950s, randomized clinical trials (RCTs) have served as the gold standard for confirming the benefits of a new drug. Accordingly, phase 3 trials, the last steps in the evaluation process for a new drug, have been recommended to all be RCTs. Nevertheless, single-arm phase 3 trials still appear to be in use.

Methods: We performed a PubMed search to identify the use of a single-arm design in phase 3 trials, excluding only non-English articles. Three categories were distinguished: past use of an RCT, of any other trial design, or no previous trial; and according to diagnosis (oncology, infection, others).

Results: A total of 176 single-arm phase 3 trials (19 oncology, 43 infections and 114 others) were identified by the search, with exponential growth since 1994, in parallel with that of RCTs. Among them, 64 (36%) were preceded by an RCT, 58 (33%) by a non-randomized trial, and 54 (31%) had no previous trial, with no main influence of the diagnosis setting. Justification of the design was reported in 30 (18%) of those trials, with ethical concerns comprising one-third of those justifications. This was similar in the 14 single-arm phase 2-3 trials, with about one-third in each group, and 17% justification of a non-comparative design.

Conclusion: The use of a single-arm phase 3 trial is heterogeneous, ranging from first trials up to confirmatory trials after a previously conducted RCT. Justification for these single-arm designs as confirmatory evidence should be more clearly reported, along with potential sources of bias.