The evaluation and validation of the three-gene signature for irinotecan sensitivity prediction. A, there was a significant association between the three-gene signature index and irinotecan sensitivity (rho = 0.71, P < 0.001). Index (Y-axis) was plotted against irinotecan inhibition rate. “0.00” stood for no inhibition, while “1.00” stood for 100% inhibition. B, ROC curve was made for irinotecan sensitivity prediction based on the three-gene signature index. Sensitivity (Y-axis) was plotted against false-positive fraction (1 - specificity). The AUC was 0.828 (95% CI: 0.755–0.901, P < 0.001). C, the irinotecan inhibition of gastric samples with sensitive-signature was much higher than those with resistant-signature (65% vs. 22%, P < 0.001). Sensitive-signature group: three-gene signature index > 0.43, n = 37; resistant-signature group: index ≤ 0.43, n = 38.