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. - Söderberg-Naucler C; Peredo I; Rahbar A; Hansson F; Nordlund A; Stragliotto G (International journal of cancer, 2014)