Lang D, et al. - In advanced non-small cell lung cancer (NSCLC) treated with single-agent PD-1/PD-L1-directed immune checkpoint inhibitor (ICI) therapy, whether serum tumor markers (STM) can serve as biomarkers for treatment monitoring and prognosis was investigated. At NSCLC diagnosis, routine measurements of carcinoembryonic antigen, carbohydrate antigen 19-9, cytokeratin-19 fragments and neuron specific enolase were obtained and initially raised markers were used for follow-up. With respect to progression-free (PFS) and overall survival (OS), researchers retrospectively analyzed leading STM alteration between ICI initiation and first subsequent restaging, taking together corresponding computed tomography assessments as per response evaluation criteria in solid tumors. Longer PFS and OS were predicted by decreasing leading STM at first restaging, and in a population of initial radiological non-responders in ICI treated NSCLC patients, those with favorable outcomes were identified by decreasing leading STM at first restaging.