Lang D, et al. - Researchers examined the value of serum tumor markers (STM) as biomarkers for therapy monitoring and for prognosis in advanced non-small cell lung cancer (NSCLC) treated with single-agent PD-1/PD-L1-directed immune checkpoint inhibitor (ICI) therapy. At NSCLC diagnosis, routine measurement of carcinoembryonic antigen, carbohydrate antigen 19-9, cytokeratin-19 fragments and neuron specific enolase is done. For the follow-up, they used initially elevated markers. According to response evaluation criteria in solid tumors (RECIST), they retrospectively analyzed leading serum tumor marker (STM) change between ICI initiation and first subsequent restaging as well as corresponding computed tomography evaluations. At first restaging, longer progression-free and overall survival were predicted by a decrease in leading STM. Among initial radiological non-responders in ICI treated NSCLC patients, patients with favorable outcomes could be identified via decreasing leading STM at first restaging. Distinctly inferior response and survival were predicted in relation to STM increase ≥2-fold. Concomitant STM decrease benefit patients with SD/PD in initial CT restaging. STM response, cerebral metastases, therapy line ≥3 are identified as the multivariate predictors of survival.