Discrepancies in endpoints between clinical trial protocols and clinical trial registration in randomized trials in oncology

BACKGROUND: Clinical trials are an essential part of evidence-based medicine. Hence, to ensure transparency and accountability in these clinical trials, policies for registration have been framed with emphasis on mandatory submission of trial elements, specifically outcome measures. As these efforts evolve further, we sought to evaluate the current status of endpoint reporting in clinical trial registries. METHODS: We reviewed 71 oncology related randomized controlled trials published in three high impact journals. We compared primary (PEP) and non-primary endpoints (NPEP) between the clinical trial protocols of these trials and their corresponding registration in one of the 14 primary global clinical trial registries. A discrepancy was defined as the non-reporting or absence of an endpoint in either the protocol or registry. The primary endpoint was the rate of discrepancy between secondary endpoints in clinical trial protocols and clinical trial registries. RESULTS: Of the 71 clinical trials, a discrepancy in PEP was found in only 4 trials (6%). Secondary endpoint (SEP) differences were found in 45 (63%) trials. Among these 45 trials, 36 (80%) had SEPs that were planned in the protocol but not reported in the registry and 19 (42%) had SEPs with endpoints in the registry that were not found in the protocol. The total number of SEPs that were absent from the corresponding registry and protocol were 84 and 29, respectively. Of these endpoints, 48 (57%) and 9 (31%) were included in the published report of these trials. CONCLUSION: Although recent regulations and enhanced procedures have improved the number and quality of clinical trial registrations, inconsistencies regarding endpoint reporting still exist. Though further guidelines for the registration of clinical trials will help, greater efforts to provide a correct, easily accessible, and complete representation of planned endpoints are needed. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12874-018-0627-2) contains supplementary material, which is available to authorized users.