Published interim results of ongoing clinical trials often report analyses without justification and may mislead clinicians about whether a particular drug or therapy is beneficial, according to a review study published in JAMA.

Investigators abstracted data from randomized trials that reported interim results of ongoing research and compared these trials with final publications. Interim results were reported in 613 of 1267 publications. In studies that reported safety or efficacy outcomes, researchers compared the trials’ characteristics, prominence, and conclusions. Trials that reported interim results were mainly focused on cardiology, oncology, or surgery.


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Overall, interim analyses enrolled fewer patients (205 vs 295 participants) and had shorter median follow-up (48 vs 104 weeks) than the final analyses. However, interim and final analyses featured similar prominence, and the majority of conclusions (79%) showed no significant change.

A total of 32 abstract conclusions reported no difference between the intervention and the comparator, and 26 discussed a beneficial effect from the intervention. Approximately 21% of the abstract conclusions did change at interim or final publication, with 4 changing from “not different” to “beneficial,” 3 from “not different” to “harmful,” and 1 from “inconclusive” to “noninferior.” According to the investigators, a change of “beneficial” to “harmful” was observed in 1 study of high-dose imatinib, which lowered event-free survival vs a standard dosing strategy.

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The limitations of this study include the lack of analyzed full text throughout the interim publications, the potential for missed publications or trials due to misclassification, and the lack of analysis of longer-term changes between the interim and final results.

Investigators suggest that the authors of interim publications should consistently use the word “interim” in the main title, include justification of the reason for publication, and should “commit to making final results accessible by linking interim publications to final reports whenever available.”


Woloshin S, Schwartz LM, Bagley PJ, Blunt HB, White B. Characteristics of interim publications of randomized clinical trials and comparison with final publications.  JAMA. 2018;319(4):404-406.