CD274 and cancer: PD-1 expression was detected in the tumour-infiltrating lymphocytes of 58.7% of patients with CUP, whereas PD-L1 expression was seen in 22.5% of cancer cells in tumours, respectively.56 In the absence of an accurate predictive biomarker for immune checkpoint inhibitors, the expression of PD-(L)1 is the rational biomarker for PD-L(1) inhibitors.