Abstract

4016 Background: The rise in early-onset gastrointestinal cancers includes an increased risk of pancreatic adenocarcinoma (PDAC), but the underlying pathogenesis is incompletely understood. The tumor microbiome is an increasing focus of research given its impact on tumor pathogenesis and outcomes. We evaluated microbiome profiles in resected specimens from early-onset PDAC (eoPDAC) and average-onset PDAC (aoPDAC). Methods: PDAC specimens were selected consecutively from Cleveland Clinic and Roswell Park Cancer Institute biorepositories and categorized on age at diagnosis ( < 50 years defined as eoPDAC, and > 50 years as aoPDAC). The tissue microbiome was characterized using shotgun metagenomic sequencing. Alpha diversity, denoting the richness and evenness of microbial species within a specific sample, was compared using the Wilcoxon rank-sum test. The differential test of Beta-diversity distances (Bray Curtis distance), representing microbial taxonomic differences between the specimens was performed using Permutational MANOVA. All p-values were adjusted for multiple testing. Results: The study comprised 44 individuals with resected PDAC (24 eoPDAC and 20 aoPDAC). After quality checks, 63 tissue specimens were selected for analysis (13 tumor and 10 adjacent normal specimens for eoPDAC, 20 each of tumor and adjacent normal specimens for aoPDAC). eoPDAC tumor demonstrated significantly higher alpha diversity compared to adjacent normal tissue (P = 0.02) and aoPDAC (P = 0.0062) while aoPDAC did not (tumor vs normal alpha diversity P = 0.31). Beta diversity analysis demonstrated significantly different diversity of genera between all the groups (P < 0.05). Consistent with this finding, the majority of the species - 259/302 (85.8%) in eo vs aoPDAC comparison and 262/366 (71.6%) for eoPDAC vs normal comparison did not overlap. Differential abundance analysis revealed a significant variation of tumor microbiome in eoPDAC vs aoPDAC (P < 0.05). Prevalent bacterial genera (tumor specimens) are listed in the Table. eoPDAC tumor tissues were enriched in Enterobacter, Neisseria,and Escherichia genera, while aoPDAC tumor tissues were enriched in Klebsiella and Bacillus genera. Conclusions: eoPDAC has a distinct microbiome profile compared to aoPDAC. The correlation with several microbial genera associated with pancreatic diseases is a significant finding and warrants further exploration. This is relevant considering the rising incidence of eoPDAC of unknown etiology, and ongoing efforts to develop microbiome-based biomarkers for screening and treatment. [Table: see text]