AbstractWith modern radiotherapy techniques, re-irradiation is a potentially curative treatment approach. However, it carries still a serious risk of severe radiation morbidity including treatment-related death. High-level evidence for an adequate treatment of these patients is still lacking since the majority of trials are retrospective. Thus, inherent biases like unbalanced patients’ characteristics in terms of the relapse intervals, sites of recurrence, and inhomogeneous re-irradiation volumes, total tumor doses, and fractionation are by definition competing risks that will flaw the validity of these studies. Hence, future well-designed prospective randomized trials are still urgently needed.