Assessing Influence of Mismatch Repair Mutations on Survival in Patients After Resection of Pancreatic Ductal and Periampullary Adenocarcinoma.

: Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer-related deaths in the United States. Previous studies have indicated that microsatellite instability and deficient mismatch repair (MMR) may be associated with improved survival in patients with pancreatic cancer. Here, we aim to investigate the impact of deficient MMR (dMMR) status on oncologic outcomes in patients after resection of PDAC and periampullary adenocarcinoma. : This is a single-institution, retrospective study based on a prospectively maintained database. Pancreatic ductal adenocarcinoma (N = 342) and periampullary adenocarcinoma patients (N = 76) who underwent pancreatic resection surgery between 2016 and 2021 were included. Immunohistochemistry staining results of MMR proteins and next-generation sequencing data were recorded. Cancer-type dependent Cox regression analyses were performed to assess overall and disease-free survival, which was complemented with a 1:2 propensity-score matching for each of the cancer types in order to compare oncologic outcomes. : A total of 418 pancreatic cancer patients were included in the analysis. Fifteen patients (3.5%) were diagnosed as dMMR (PDAC N = 7 and periampullary adenocarcinoma N = 8). Cox regression modeling of dMMR status interaction with TNM staging and cancer type revealed that dMMR status strongly improves overall survival ( < 0.05). After propensity-score matching, Cox regression identified dMMR status as a significant marker of improved overall survival (HR = 0.27, 95%CI 0.09-0.88, = 0.029). : Overall, our findings suggest that dMMR status is associated with markedly improved survival outcomes in patients after resection of pancreatic and periampullary cancer. Future large-scale studies are needed to further validate this finding.