By combining the efficacy data of the SKKU AGC cohort and the SYSUCC AGC cohort, multivariable logistic regression analysis indicated that ecDNA amplification (P = 0.02) is a negative predictor of anti-PD1 treatment response in advanced gastric cancer, independent of the known responsive indicators PDL1 status (P < 0.001) and tumor mutation burden (TMB) (P = 0.02, Supplementary Fig. 11). Here, CD274 is linked to gastric cancer.