The largest studies so far, investigating the role of PD-L1+ CTCs in the clinical setting, were conducted by Ilié et al. [28] and Janning et al. [29], who utilized a sized based CTC-enrichment approach (Isolation by SizE of Tumor cells (ISET), Rarecells Diagnostics SAS) with, respectively, the FDA-approved EpCAM-based CellSearch® System (Menarini Silicon Biosystems Inc, Huntingdon Valley, PA, USA and the epitope-independent ParsortixTM system (Angle, Guildford, UK) followed by immunostaining of retained cells. This evidence concerns the gene CD274 and neoplasm.