Early stopping rules--clinical perspectives and ethical considerations.

A clinical trial should only be launched in the presence of equipoise both amongst clinicians responsible for treating the disease and their patients. However, during the period of patient recruitment the chances are that the levels of equipoise will modify. In some cases, where toxicity or inferiority of efficacy are readily demonstrable, the trial needs to be stopped prematurely to prevent harm to patients. In other cases, the degree of equipoise may be increased by the very existence of the trial or from conflicting evidence reported from other studies. By reference to four specific trials it is argued that instead of definitive rules, the decision as to whether recruitment should be continued must be the role of a Data Monitoring Committee which is able to consider and respond to all the available evidence.