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Survival Analysis — SCE Medical Oncology MCQ

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HardClinical Trials & StatisticsSurvival AnalysisSCE Medical Oncology

A researcher is interpreting Kaplan-Meier survival curves for a new immunotherapy trial. The curves show initial overlap for the first 6 months then progressive separation favouring the immunotherapy arm. This pattern is described as a 'delayed separation' of curves. What is the implication for the log-rank test?

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Correct answer: D — The log-rank test may underestimate the treatment effect because it gives equal weight to all time points; a weighted log-rank test or restricted mean survival time (RMST) analysis may be more appropriate

The standard log-rank test assumes proportional hazards (constant HR over time). Delayed separation of Kaplan-Meier curves (characteristic of immunotherapy trials where early events are similar but late benefit emerges) violates this assumption. The log-rank test gives equal weight to all time points, potentially diluting the signal. Alternative analyses include: weighted log-rank tests (e.g. Fleming-Harrington), RMST (restricted mean survival time) and piecewise Cox models. These have been increasingly used in ICI trial analyses.

Reference: JRCPTB Medical Oncology Curriculum; Trinquart et al JCO 2016; ESMO Statistical Methods