Intense FOXP3+ lymphocyte infiltration relates to poor prognosis,22 and indeed this has been documented in patients with NSCLC.23–28 In a recent study, we found that tumour infiltration by FOXP3+ Tregs occurs early in the development of NSCLC, and adversely affects the post-operative outcome.15 Tregs may compromise the activity of immune-checkpoint inhibitors, so that assessment of their presence could be a useful marker to guide immunotherapy. Here, FOXP3 is linked to non-small cell lung carcinoma.