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Clinical Roundup

Study raises concerns about clinical trial bias from undisclosed censoring

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A University of Toronto-led study found that only 59% of oncology clinical trials studied provided adequately-defined rules for censoring.

The study, “Quantifying Withdrawal of Consent, Loss to Follow-Up, Early Drug Discontinuation, and Censoring in Oncology Trials,” was published in the Journal of the National Comprehensive Cancer Network.

The researchers examined published randomized control trials supporting FDA approval for treatments for solid tumors from Jan. 2015 through Dec. 2019—and found that for 33 out of 81 studies, it was not clear in the publication why or how patients were being censored.

Censoring is defined in this context as the practice of removing patients from follow-up before experiencing the outcome of interest; for instance, if the main outcome of a cancer treatment trial is survival and the patient experiences a heart attack and withdraws from the trial, they may no longer be followed up on.

If the proportion of patients who are censored is not evenly balanced between comparison groups, this can introduce bias and makes it difficult to interpret the results of trials.

“We hope that our findings will prompt investigators and journals to report early drug discontinuation, withdrawal of consent, loss to follow-up, and censoring more transparently in trial publications,” lead researcher Brooke E. Wilson of the University of Toronto said in a statement. “This would allow patients and clinicians to make more informed decisions regarding the potential benefits of a treatment.”

The authors compiled a list of goals and recommendations to improve transparency and reporting in clinical trials, including: 

  • Minimize the chance of post-randomization bias
  • Improve transparency regarding censoring methods in oncology trials
  • Explore the impact of censoring on trial results
  • Improve the handling of transparency of missing outcome data in trial results
  • Acknowledge the potential impact of censoring on the interpretation of results
  • Provide transparent information regarding early drug discontinuation and withdrawal of consent or loss to follow-up
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