Background: Pancreatic cancer (PC) is the third leading cause of cancer death in the United States. The high mortality associated with PC is attributed to multiple reasons: lack of effective therapies, aggressive biology and late diagnosis. Due to the absence of reliable early disease biomarkers, PC screening is largely dependent on imaging. Recent studies have highlighted the importance of the gut and tumor microbiome in PC. We present here the first report of oral and gut microbiome prospective analysis of PC high-risk individuals (PC-HRI) undergoing screening. Methods: We collected periodontal and stool samples at the University of Texas MD Anderson Cancer Center from 2017-2022. A total of 448 samples, consisting of 250 oral and 198 gut samples were obtained. Samples were collected from PC (n=73), PC-HRI (n=34), and healthy (n=143) individuals. 16s rRNA sequencing was used to characterize the oral and gut microbiome and statistical analysis and correlation with imaging and clinical characteristics were performed. Results: We identified three phyla, namely Proteobacteria, Actinobacteria, and Fusobacteria as significantly more abundant in the gut microbiome of PC patients. Conversely, Proteobacteria was decreased in the oral microbiome of PC patients. At the class level, Gammaproteobacteria (GP) oral/gut ratio was significantly decreased in PC patients compared with healthy individuals (p=0.02). Analysis of PC-HRI revealed also low GP oral/gut ratio in high-risk individuals who were diagnosed with worrisome pancreatic focal lesions. Interestingly, Gammaproteobacteria (GP) is one of the main classes of bacteria detected in pancreatic cancer tissue. GP shifts in oral and gut environments could be implicated in pancreatic early tumorigenesis and serve as biomarker of the disease. Additionally, gut bacteria with metabolic pathways related to lipid metabolism were more enriched in PC patients and PC-HRI with focal lesions compared to healthy controls. Conclusions: Gammaproteobacteria oral/gut ratio represents a potential novel biomarker which could predict presence of early high risk-pancreatic focal lesions in PC-HRI. Taken together, this report provides observational evidence about changes in oral and gut microbiome in patients with pancreatic cancer but even more importantly, the fact that those changes could be detected in PC-HRI with early high-risk lesions. Broader validation in other high-risk cohorts would be required. Detection of GP oral/gut ratio would represent an inexpensive, non-invasive method that could be useful for PC screening. Functional studies should be performed to determine how GP shifts can contribute with pancreatic tumorigenesis. Research supported by CPRIT (Grant Number: RP200173) and philanthropic funding through the MD Anderson Moonshot Program.