The role of censoring on progression free survival: oncologist discretion advised

Censoring is increasingly appreciated as a potential bias affecting estimates of progression free survival (PFS) in randomised trials. In this commentary, we explore the central assumption of censoring. Censored patients are considered no more or less likely to undergo the event of interest than those who remain in the analysis. Instead however, if one makes alternate assumptions, that censored patients are different than those who remain on the trial, estimates of PFS change. Using the example of the recent BOLERO-2 trial of exemestane and everolimus, we show that by altering the assumptions for censoring, the major conclusions of clinical trials may change. As such, the number of censored patients at each time interval should be routinely reported in randomised trials to better understand the implications of censoring.