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Stopping Clinical Trials Early Often Exaggerates Treatment Effects

An international study of nearly 100 clinical trials that were stopped early due to positive treatment effects has found that many of those effects were exaggerated.

The authors of the study -- published in the current issue of the Journal of the American Medical Association -- recommend that researchers resist pressures to end clinical trials early and continue trials for longer periods before even considering premature termination.

“Our research shows that in most cases early stopping of clinical trials resulted in misleading estimates of treatment effects. These misleading estimates are likely to result in misguided decisions about the trade-off between risks and benefits of a therapy,” says Victor Montori, M.D., Mayo Clinic endocrinologist and corresponding author of the study. “On average, treatments with no effect would show a reduction in relative risk of almost 30 percent in stopped early trials. Treatments with a true relative risk reduction of 20 percent would show a reduction of over 40 percent.”

The clinical trials that Dr. Montori and colleagues studied were ended early because of a convincing -- and usually large -- apparent difference between an experimental treatment and an existing standard therapy. The studies were ended so participants taking a placebo or less effective medications could also take the studied drug. It usually also allows physicians to prescribe the therapy sooner because it will reach the market earlier.

Dr. Montori says almost everyone involved benefits from a trial ending early -- doctors, researchers, funding sources, pharmaceutical firms, scientific journals, even reporters -- everyone except the patient, who may end up receiving a therapy on the basis of misleading information about its benefits.

The researchers examined 63 medical questions regarding 91 truncated trials and compared them to 424 comparable trials that were not stopped early. Results showed that the studies that were stopped -- especially smaller trials of a few hundred participants -- had exaggerated or misleading treatment effects. Those misleading findings are often compounded downstream because researchers are less likely to return to the topic after what is perceived as a significant successful finding.

The authors recommend that researchers use restraint and truncate clinical trials only near the end of a study and then only with “a very good reason.” Otherwise, says Dr. Montori, patients and physicians will be making treatment choices based on inaccurate information, or worse, opting for one treatment when another may be more appropriate.

The study was supported by the Medical Research Council of the U.K. Other authors include Dirk Bassler, M.D.; Matthias Briel, M.D.; Qi Zhou, Ph.D.; Stephen Walter, Ph.D.; Gordon Guyatt, M.D.; and Diane Heels-Ansdell, all of McMaster University, Ontario; Melanie Lane, Mayo Clinic; and Paul Glasziou, M.B.B.S., Ph.D., University of Oxford, England.

About Mayo Clinic
For more than 100 years, millions of people from all walks of life have found answers at Mayo Clinic. These patients tell us they leave Mayo Clinic with peace of mind knowing they received care from the world's leading experts. Mayo Clinic is the first and largest integrated, not-for-profit group practice in the world. At Mayo Clinic, a team of specialists is assembled to take the time to listen, understand and care for patients' health issues and concerns. These teams draw from more than 3,700 physicians and scientists and 50,100 allied staff that work at Mayo Clinic’s campuses in Minnesota, Florida, and Arizona; and community-based providers in more than 70 locations in southern Minnesota, western Wisconsin and northeast Iowa. These locations treat more than half a million people each year. To best serve patients, Mayo Clinic works with many insurance companies, does not require a physician referral in most cases and is an in-network provider for millions of people. To obtain the latest news releases from Mayo Clinic, go to For information about research and education, visit ( is available as a resource for your general health information.

Robert Nellis | Newswise Science News
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