MMR‐deficient pancreatic cancer patients had longer postsurgical survival, higher TMB, and greater neoantigen loads. MMR‐deficient tumors were also less likely to have traditional PDAC mutations such as KRAS and SMAD4, and more likely to have mutations in ACV2RA and JAK1 which are associated with MSI. This evidence concerns the gene JAK1 and familial pancreatic carcinoma.