Patient preference trials in oncology: a scoping review and recommendations on reporting

The feasibility, generalizability, and validity of randomized controlled trials (RCTs) may be compromised when patients have preferences for specific trial arms. The patient preference trial (PPT) design, which assigns at least a subset of the patients based on their preference rather than randomization, has been proposed as an alternative. The aim of this review was to provide an overview of the application of the PPT design in oncological research, with a particular focus on PPTs designed to assess the effectiveness of an intervention and provide recommendations on reporting.

We performed a scoping review including all prospective oncological studies where trial arm allocation for part or all of the patients was based on patients' preferences. Retrieved information included research objectives, motivation for the design choice, baseline covariate adjustments, and sample size calculations.

We identified 44 PPTs, of which 34 (77%) aimed to investigate intervention effectiveness and were reviewed in more detail. Of these 34 effectiveness PPTs, 24 (71%) studies were completed trials, while 10 were protocols. The most frequently indicated rationale behind opting for the PPT design was the perceived infeasibility of an RCT (17 [50%] studies). Baseline covariate adjustment was performed in 18 (53%) studies. Fourteen out of 24 completed trials reported an unequal allocation ratio across trial arms not anticipated during the design.

This review identified several challenges for PPTs in oncology. Future PPTs should take bias due to confounding and unequal group sizes arising from the preferential allocation into account and report on these issues, as these aspects are crucial for the validity and statistical power of the study.