Use of Cox regression with treatment status as a time-dependent covariate to re-analyze survival benefit excludes immortal time bias effect in patients with glioblastoma who received prolonged adjuvant treatment with valganciclovir

摘要

In a letter to the Editor, Liu and Hu1 commented on our studies demonstrating a potential survival benefit in glioblas-toma patients who received prolonged treatment with valgan-ciclovir for cytomegalovirus (CMV) infection in their tumor as add on to their standard oncology treatment. Liu and Hu raised the question of whether so-called immortal-time bias could explain the highly improved survival observed in treated patients. Indeed, with a retrospective design and a definition of exposure that requires a minimum time of exposure, there is a risk of immortal time bias, since those qualifying for exposure by definition are given a certain degree of immortal time.4 Hence, Liu and Hu's call for re-analysis of our data using Cox regression with treatment status as a time-dependent covariate is justified. Here we present the outcome of that re-analysis.