Oral Microbiota and Carcinogenesis: Exploring the Systemic Impact of Oral Pathogens

For decades, cancer risk has been explained mainly by local factors. However, emerging evidence shows that the oral microbiome acts as a systemic modifier of oncogenesis well beyond the head and neck. This review synthesizes clinical and mechanistic data linking dysbiotic oral communities, especially <i>Porphyromonas gingivalis</i>, <i>Fusobacterium nucleatum</i>, and <i>Treponema denticola</i>, to malignancies across gastrointestinal, respiratory, hepatobiliary, pancreatic, breast, and urogenital systems. We summarize organ-specific associations from saliva, tissue, and stool studies, noting the recurrent enrichment of oral taxa in tumor and peri-tumoral niches of oral, esophageal, gastric, colorectal, lung, pancreatic, liver, bladder, cervical, and breast cancers. Convergent mechanisms include the following: (i) persistent inflammation (lypopolysacharide, gingipains, cytolysins, and collagenases); (ii) direct genotoxicity (acetaldehyde, nitrosation, and CDT); (iii) immune evasion/suppression (TLR/NLR signaling, MDSC recruitment, TAN/TAM polarization, and TIGIT/CEACAM1 checkpoints); and (iv) epigenetic/signaling rewiring (NF-κB, MAPK/ERK, PI3K/AKT, JAK/STAT, WNT/β-catenin, Notch, COX-2, and CpG hypermethylation). Plausible dissemination along an oral-gut-systemic axis, hematogenous, lymphatic, microaspiration, and direct mucosal transfer enables distal effects. While causality is not yet definitive, cumulative data support oral dysbiosis as a clinically relevant cofactor, motivating biomarker-based risk stratification, saliva/stool assays for early detection, and microbiome-targeted interventions (periodontal care, antimicrobials, probiotics, and microbiota modulation) alongside conventional cancer control.