The reason that immune checkpoint inhibitors have not been widely applied to pancreatic cancer treatment is probably because of low immunogenicity or dense stromal fibrosis. Recently, only pembrolizumab was recommended for DNA mismatch repair deficiency or high microsatellite instability by National Comprehensive Cancer Network guideline. Pancreatic ductal adenocarcinoma (PDAC) accounts for more than 90% of pancreatic cancer, with a poor overall survival rate, the value of immunotherapy for PDAC needs more research. Here, we report a 56-year-old man suffered from PDAC with liver metastasis after radical surgery. The next-generation sequencing result demonstrated that it had remarkably high tumor mutational burden (TMB) of 49.92 Muts/Mb and microsatellite stability. Sintilimab (anti-PD-1) monotherapy was continuously administrated after failure of combined chemotherapy in second line, achieving stable disease within 22 months and few immunotherapy-related adverse events. To our knowledge, this is the first time to report a good outcome achieving 22 months with progression-free survival after PDAC metastasis with monotherapy of sintilimab. TMB may serve as a potential efficacy-related predictor in PDAC patients with sintilimab and help physicians make optimum clinical strategy.Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc.