In this study, PD-L1 expression and the presence of mutant GTF2I were inversely correlated; very few patients were positive for both PD-L1 and mutant GTF2I. In addition, blood marker data (serum LDH and PLR) in our study suggested that thymomas without the GTF2I mutation exhibited a higher response rate to immunotherapy. Here, GTF2I is linked to thymoma.