A study published in PLOS ONE last week attempted to characterise the reasons why trials (listed on http://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).