A study published in PLOS ONE last week attempted to characterise the reasons why trials (listed on www.clinicaltrials.gov) were terminated, and also examined the availability of results from these trials.
The majority (68%; 619/905) of trials with results were terminated for reasons other than scientific data (Table 1). Within this category, 11% of the trials were terminated for reasons considered external to the trial (external information; product withdrawal) while the remaining 89% of trials were terminated for reasons directly related to trial conduct or logistics. Insufficient rate of accrual was the leading sub-category, representing 57% of trials terminated for other reasons. Twenty-one percent of trials were terminated based on scientific data from the trial (e.g., findings related to the overall benefit-risk profile of the intervention(s) evaluated).
Overall, data for a primary outcome measure were available on ClinicalTrials.gov and in the published literature for 72% and 22% of trials, respectively. Primary outcome data were reported on the ClinicalTrials.gov results database and in the published literature more frequently (91% and 46%, respectively) when the decision to terminate was based on data from the trial (see table below).