- Group sequential trials that stop early for efficacy tend to overstate the evidence for efficacy. While true, this can be corrected easily, and should be. Standard texts on group sequential trials, and software make the application of this correction easy.
- Trials that stop early tend to have too little evidence for safety.
The second point about safety is a major one, and one where the industry would do better to keep up with the methodology. Safety analysis is usually descriptive because hypothesis testing doesn't really work so well, because Type I errors (claiming a safety problem where there is none) is not as serious a problem as a Type II error (claiming no safety problem where there is one). Because safety issues can take many different forms (does the drug hurt the liver? heart? kidneys?) there is a massive multiple testing problem, and efforts to control the Type I error that we are used to are no longer conservative. There is the general notion that more evidence is better (and, to an extent, I would agree), but I think it is better to solve the hard problem and attempt to characterize how much evidence we have of the safety of a drug. We have started to do this with adverse events; for example, Berry and Berry have implemented a Bayesian analysis that I allude to in a previous blog post. Other efforts include using False Discovery Rates and other Bayesian models.
We are left with another difficult problem: how much of a safety issue are we willing to tolerate for the efficacy of a drug? Of course, it would be lovely if we could make a pill that cured our diseases and left everything else alone, but it's not going to happen. The fact of the matter is that during the review cycle regulatory agencies have to make the determination of whether safety risk is worth the efficacy, and I think it would be better to have that discussion up front. This kind of hard discussion before the submission of the application will help inform the design of clinical trials in Phase 3 and reduce the uncertainty in Phase 3 and the application and review process. Then we can talk with a better understanding about the role of sequential designs in Phase 3.