IDO1 and neoplasm: This is partly due to the heterogeneous tumour biology of carcinogen-induced malignancies and partly because this cancer attracts little research interest and spending (0.8% of cancer research spend in 2018/2019).14 There are potential prognostic markers under investigation: either patient based (tobacco use, muscle mass) or tumour driven (the immune checkpoint inhibitor complex IDO, ‘immunoscore’, PDL-1).