Exosomal PD-L1 levels were increased significantly after 5-FU treatment, with maximum value after treatment at 1.0 μg/ml 5-FU for 48 h and 0.1 μg/ml for 72 h (Figure 2E), indicating that 5-FU caused gastric cancer cells to produce exosomal PD-L1. This evidence concerns the gene CD274 and gastric cancer.