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Study Examines Possible Clinical Trial Bias From Undisclosed Censoring


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New research published by Wilson et al in JNCCN–Journal of the National Comprehensive Cancer Network found that only 59% of oncology clinical trials studied provided adequately defined rules for censoring. The researchers examined published randomized control trials supporting U.S. Food and Drug Administration approval for treatments for solid tumors from January 2015 through December 2019; they 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 with. 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. This would allow patients and clinicians to make more informed decisions regarding the potential benefits of a treatment,” said lead researcher Brooke E. Wilson, MBBS, MSc, of the University of Toronto. “Regulatory authorities and journals can play a leadership role in mandating improved transparency and ensuring that censoring data be made publicly available.”

Improving Transparency and Reporting

The authors compiled a list of goals and recommendations to improve transparency and reporting in clinical trials. Those goals include:

  • Minimizing the chance of post-randomization bias
  • Improving transparency regarding censoring methods in oncology trials
  • Exploring the impact of censoring on trial results
  • Improving the handling of transparency of missing outcome data in trial results
  • Acknowledging the potential impact of censoring on the interpretation of results
  • Providing transparent information regarding early drug discontinuation and withdrawal of consent or loss to follow-up.

“In trials with survival outcomes, it’s important to clearly and carefully define censoring,” commented Elizabeth A. Handorf, PhD, Associate Research Professor at Fox Chase Cancer Center, who was not involved in this research. “It’s possible that different ways of defining or handling censoring could change the results. It’s concerning that so few studies presented sensitivity analyses, as this is the best way for the reader to understand the potential impact of the study’s definitions and assumptions. I was surprised to see that 54 studies had a planned sensitivity analysis for censoring rules, but only 3 published the results. Even if a sensitivity analysis shows no difference, those results are useful to include.”

Disclosure: For full disclosures of the study authors, visit jnccn.org.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
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