Monitoring for lack of benefit: a critical component of a randomized clinical trial.

To balance patient interests against the need for acquiring evidence, ongoing randomized clinical trials are formally monitored for early convincing indication of benefit or lack of benefit. In lethal diseases like cancer, where new therapies are often toxic and may have limited preliminary efficacy data, monitoring for lack of benefit is particularly important. We review the complex nature of stopping a randomized trial for lack of benefit and argue that many cancer trials could be improved by a more aggressive approach to monitoring. On the other hand, we caution that some commonly used monitoring guidelines may result in stopping for lack of benefit even when a nontrivial beneficial effect is observed.