Music M, et al. - Among patients (n = 24) treated with pembrolizumab, researchers investigated potential predictive biomarkers of response and/or toxicity by analyzing pre and postimmunotherapy serum samples for alterations in PD-1 and over 1,000 additional protein markers. According to the selection criteria, either a > 4-fold increase or 4-fold reduction in expression after immunotherapy must be present in at least two patients within any of three patient groups [responders without immune-related adverse events (irAEs), responders with irAEs or non-responders with irAEs]. As technical duplicates, female and male control samples were analyzed. In this study, increased serum PD-1 was detected after pembrolizumab therapy but without any predictive value for response or toxicity.