Inherent problems with randomized clinical trials with observational/no treatment arms

Randomized clinical trials (RCTs) offering an observation/no treatment (OBS/NoRx) arm as control and which are focused on the management of a condition with potentially life-threatening consequences, however small the risk, often experience a significant rate of crossover to treatment by those randomized to the OBS/NoRx arm. Results of these trials when analyzed on intent-to-treat basis often fail to resolve the issue at which they were directed. The authors have observed this in trials of abdominal aortic aneurysms with this design and use these to exemplify the dilemmas RCTs of such design create, with crossovers ranging from 27% to over 60% (EVAR II, UKSAT, ADAM, PIVOTAL). Results of these trials are frequently used as level I medical evidence and their potential impact on clinical decision making and reimbursement can be quite significant and long-lasting. Recommendations regarding trial end points and suggestions to mitigate the high crossover effect are offered. It may be that some clinical conditions dealing with potentially life-threatening problems should not be studied in randomized prospective clinical trials containing an OBS/NoRx arm.