CD274 and lung cancer: We next examined the concordance of PD-L1 staining between CTCs and tumor biopsy sections, as PD-L1 positivity in these sections has been shown to be a predictor for outcome in lung cancer and the PD-1 inhibitor pembrolizumab requires a patients’ tumor biopsy to be positive for PD-L1 prior to administration (as determined by an FDA-approved companion diagnostic).