Exposure to 2.5 µm particulate matter (PM2.5) increases the risk of non-small-cell lung cancer in non-smoking individuals with EGFR mutations. At ESMO 2022 Charles Swanton (Translational Cancer Therapeutics Department – Francis Crick Institute, London) explained that this effect is driven by an influx of macrophages and an increase in the inflammatory mediator interleukin-1β, which promotes carcinogenesis in airway cells. We asked Swanton why the trial TRACERx is so important.