Cytokine levels have been evaluated in earlier studies of immune checkpoint inhibitors, with primary focus on antitumour efficacy.26 One study of preoperative ipilimumab for melanoma found that baseline interleukin-17 was associated with the development of diarrhoea/colitis.27 That we identified a different pattern of cytokines in the present study may reflect the predominance of anti-PD1/PDL1 therapy and low rates of gastrointestinal toxicity (which is more commonly associated with anti-CTLA4 treatment). This evidence concerns the gene CTLA4 and melanoma.