In this study, the ISET (Isolation by SizE of Tumor cells, Rarecells Diagnostics SAS) technology followed by Giemsa and immunostaining was utilized to detect PD-1+ and PD-L1+ CTCs in metastatic NSCLC patients before (chemotherapy-naïve, n = 30) and after chemotherapy (after the third chemotherapy cycle at the time of assessment of treatment efficacy, n = 11). The gene discussed is PDCD1; the disease is non-small cell lung carcinoma.