The aim of the study was to determine DNA mismatch repair (MMR) proteins byimmunohistochemically using MLH1, MSH2, MSH6, and PMS2 antibodies in patientsdiagnosed as pancreatic ductal adenocarcinoma and to assess its relationship withhistopathological and clinical prognostic parameters. Fifty cases with a diagnosis ofpancreatic ductal adenocarcinoma who underwent surgical resection, were included inthe study. Demographic and histopathological features of the patients were collectedfrom the medical records. The relationships between microsatellite status and prognosticparameters were determined. The mean age of the patients was 66.5 +/- 9.5 years (range:47-87) and male/female ratio was 1.63 (31/19). No errors were detected in DNA MMRproteins in any of the cases, and were classified as microsatellite stable. The mean tumordiameter was 4.01 +/- 1.77 cm and 74% of the tumors were localized in the pancreatichead. All of the cases had lymphatic invasion, whereas vascular invasion was detected inonly 78% and perineural invasion in 98% of the patients. When the relationship betweenprognostic parameters and survival was evaluated, statistically significant correlation wasobserved in patient age and histopathological parameters such as tumor diameter, statusof surgical margins, and vascular invasion (p< 0.05). Age, tumor size, presence of tumor atsurgical margins, vascular invasion, and adjuvant treatment were correlated with survival.Although microsatellite instability was not detected in our cases, it is important todetermine the microsatellite status by immunohistochemistry for predicting thechemotherapy response and determining the immunotherapy option in pancreaticadenocarcinomas