CD274 and lung carcinoma: These were found after searching for CTC studies and PD-L1 expression in National Center for Biotechnology Information (NCBI) PubMed using both circulating tumour cells and PD-L1 related terms together (‘CTC’, ‘programmed death ligand 1′, or ‘programmed cell death ligand 1′), disease terms (‘lung cancer or non-small cell lung cancer’ or ‘NSCLC’), and combined terms.