| Summary: | Treatment switching can occur when patients in the control group of a clinical trial are allowed to switch onto the experimental treatment at some point during follow-up. Switching is common in clinical trials of cancer treatments and can also occur in trials of treatments for other diseases. When switching occurs, an "intention to treat" (ITT) analysis - whereby the data are analysed according to the arms to which patients were randomised - of the overall survival (OS) advantage associated with the new treatment will be biased: If control group patients switch treatments and benefit from the new treatment the OS advantage of the new treatment will be underestimated. Various statistical methods are available to adjust survival estimates in the presence of treatment switching, but each makes important assumptions and is subject to limitations. This Technical Support Document (TSD) introduces Rank Preserving Structural Failure Time Models (RPSFTM), Iterative Parameter Estimation (IPE), Inverse Probability of Censoring Weights (IPCW) and other adjustment methods that may be used in the presence of treatment switching
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