Forty-five patients with MSI-H/dMMR GI tumors, including gastric cancer, colorectal cancer, cholangiocarcinoma, small intestine cancer, pancreatic cancer, and duodenal cancer, receiving PD-1 blockade were analyzed....PTEN mutations, which were mutually exclusive with a low TMB, were significantly associated with a lower ORRs than wild-type PTEN (21.4 vs 54.8%; odds: 4.45, P = 0.045)....Low TMBs and PTEN mutations...negative predictors of PD-1 blockade responses in patients with MSI-H/dMMR GI tumors.