Guibert N, et al. - Researchers hypothesized that liquid biopsy with PD-L1 analysis on circulating tumor cells (CTCs) from patients with non-small cell lung cancer (NSCLC) might overcome the limitation regarding patient selection, based on PD-L1 expression on tumor tissue, for PD-1/PD-L1 inhibitor therapy. In patients with advanced NSCLC treated with nivolumab, baseline PD-L1 expression could be assessed on 72% and 93% of tissue and CTC, respectively. Overall, it was feasible to assess PD-L1 expression in CTCs and CTCs are more often positive than in tissue. In patients treated with PD-1 inhibitors, an association of pre-treatment PD-L1+CTCs with bad prognosis was observed.