Although PD-L1 expression in tumours is considered a diagnostic marker for anti PD-1 antibodies (such as pembrolizumab) in non-small cell lung cancer,28 it is still unclear whether PD-L1 expression is a prognostic marker for all immune-targeting therapies based on PD-1/PD-L1 blockade in various types of cancer. The gene discussed is PDCD1; the disease is cancer.