Non-small cell lung cancer （NSCLC） is a malignant tumor with a high global incidence rate， accounting for about 10.54% of all new cancer cases and posing a serious threat to human health. Due to significant individual variations in the efficacy of immunotherapy among NSCLC patients， it is necessary to identify accurate detection indicators to screen appropriate populations， monitor treatment efficacy， and assist in prognosis assessment. Programmed death-ligand 1 （PD-L1）， as an immunosuppressive molecule expressed on the surface of tumor cells and various immune cell membranes， can serve as a "companion diagnostic" or "supplementary diagnostic" tool to guide clinical treatment decisions for metastatic NSCLC patients. Given that tumor tissue PD-L1 testing is an invasive procedure and its reliability is still under debate， the assessment of PD-L1 expressionvialiquid biopsies， such as circulating tumor cells， will play a significant role in predicting treatment response and prognosis in NSCLC patients.