Does Time to Treatment Failure Measure the Same Clinical Process Across Oncology Facilities? Comment on Kajiura et al. Facility-Level Medical Oncology Specialist Availability and First-Line Time to Treatment Failure in Lung Cancer: A Nationwide C-CAT Registry Analysis. Curr. Oncol. 2026, 33, 462

Time to treatment failure (TTF) is a pragmatic endpoint that captures treatment discontinuation for multiple reasons. In a recent nationwide C-CAT registry analysis, Kajiura et al. examined whether facility-level medical oncology specialist availability was associated with first-line TTF among patients with lung cancer. We highlight two considerations that may influence the interpretation of facility-level differences in TTF: the heterogeneous reasons underlying treatment termination and the post–first-line selection inherent to C-CAT registration. Examining treatment-ending reasons and the timing of C-CAT registration across specialist-availability groups may help clarify whether differences in TTF reflect treatment duration itself or differences in cohort composition and treatment-discontinuation processes.