Pancreatic Cancer in the Holobiont and Therapeutic Targets: A Review

Increasing evidence suggests pancreatic cancer develops within a host-microbe ecosystem in which microbial communities across anatomical niches interact with tumour biology, immune regulation, metabolism, and therapeutic response. This review examines pancreatic cancer through the lens of humans as holobionts, integrating evidence from the oral, gut, biliary, and intratumoural microbiomes. Epidemiological and sequencing studies demonstrate consistent microbial alterations across these niches in pancreatic cancer, including oral dysbiosis associated with periodontal pathogens, gut microbial shifts toward pro-inflammatory taxa, disease-specific biliary microbial signatures, and the presence of distinct intratumoural microbial communities. Mechanistic studies indicate that intestinal barrier disruption, microbial translocation, immune and metabolite signalling can influence tumour immune architecture, macrophage polarisation, T-cell infiltration, oncogenic signalling pathways, and chemotherapeutic metabolism, particularly inactivation by tumour-associated bacteria. Microbiome-driven shifts in immunometabolism can reprogramme immune-cell metabolic pathways, impairing effective T-cell activation, promoting tumour-supportive macrophage phenotypes. Emerging therapeutic strategies aim to modulate the microbiome-tumour axis, including dietary interventions, probiotics and immunonutrition, faecal microbiota transplantation, engineered microbial therapies, and microbiome-informed antibiotic strategies. While pre-clinical findings are compelling and early-phase clinical studies suggest feasibility, most evidence remains associative and heterogeneous across cohorts and methodologies. Understanding pancreatic cancer as a multi-site ecological system may help explain inter-patient variability in disease progression and treatment response. This could usher in a new era for therapeutic manipulation where future progress will depend on longitudinal, multi-omic, and interventional studies to determine whether microbiome-targeted strategies can produce clinically meaningful improvements in pancreatic cancer outcomes.