A pragmatic, adaptive clinical trial design for a rare disease: The FOcal Cerebral Arteriopathy Steroid (FOCAS) trial.

backgroundPediatric stroke investigators identified as their top research priority a clinical trial of corticosteroids for focal cerebral arteriopathy (FCA). However, FCA is both rare and an acute condition making it infeasible to enroll the large sample sizes needed for standard, confirmatory clinical trials. We present a pragmatic approach to clinical trial design that may inform the approach to other rare disorders.

methodsWe surveyed pediatric stroke experts to determine the level of evidence that would impact their clinical management of FCA. Incorporating survey results, a randomized, group sequential Bayesian adaptive design was proposed based on a quantitative radiologic outcome measure (change from baseline in change in the FCA Severity Score). Using accumulating information, the design determines whether intervention is better than control with high probability.

resultsAmong 21 (100%) respondents, the probability of corticosteroid efficacy that would lead the experts to treat was 30% (median). The probability of efficacy that would make them unwilling to randomize (because they would feel all children should receive corticosteroids) was 70%. Simulation studies with the proposed design showed that a total of 42 subjects controls the type I error rate at the desired level 0.20 and yields a smaller average sample size and trial duration compared to a conventional design.

conclusionsDesigns in rare diseases require special considerations; this is especially true for this childhood disease, which is both uncommon and acute. This design has incorporated expert consensus to establish the criteria for success, formal monitoring rules for safety, and early stopping rules.