In a phase I study of atezolizumab for patients with advanced melanoma, elevated expression of IFN-γ as well as IFN-γ-inducible genes (for example, indoleamine 2,3 dioxygenase 1 [IDO1] and C-x-C motif chemokine ligand 9 [CXCL9]) in pre-treatment tumours were demonstrated in responding patients (59). The gene discussed is IDO1; the disease is melanoma.