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Immune Flare Halo — SCE Medical Oncology MCQ

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HardLung CancerImmune Flare HaloSCE Medical Oncology

A 70-year-old man with NSCLC on pembrolizumab achieves a partial response. At restaging, his CT shows decreased tumour size but new ground-glass changes around the tumour (halo sign). He is asymptomatic. What does this represent?

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Correct answer: A — Tumour pseudoprogression or peri-tumoural inflammation from immune activation — the halo of ground-glass may represent immune cell infiltration around a responding tumour; continue treatment with close follow-up imaging at 4-6 weeks

Peri-tumoural ground-glass changes (immune flare) around a responding tumour on immunotherapy represent immune cell infiltration and are not progressive disease. This pattern, combined with decreasing tumour density/size at the centre, is consistent with immune-mediated response. iRECIST criteria allow treatment continuation beyond initial apparent progression with confirmatory scanning at 4-6 weeks. Premature treatment discontinuation based on misinterpreted imaging can deny patients ongoing ICI benefit.

Reference: ESMO 2024 NSCLC; iRECIST Seymour et al Lancet Oncol 2017