Factors leading to PD-L1 expression in melanoma tumour tissues are complicated by the fact that cytokines secreted from TILs frequently induce PD-L1 expression in tumour cells, which masks whether cytokine-independent, tumour cell-intrinsic PD-L1 expression (i.e., PD-L1 constitutive expression, or PD-L1CON) has occurred. The gene discussed is CD274; the disease is melanoma.