Bacterial contributions to cancer development: mechanisms, dysbiosis, and cross-cancer associations

Cancer is a multifactorial disease influenced by complex interactions between genetic, environmental, and microbial factors. Growing evidence demonstrates that several bacterial species contribute to carcinogenesis through chronic inflammation, production of genotoxic metabolites, disruption of cell-cycle regulation, and modulation of host immune responses. Helicobacter pylori–induced gastric adenocarcinoma remains the most well-established example of bacteria-driven oncogenesis; however, accumulating studies indicate that additional virulence mechanisms and bacteria-dependent pathways are also implicated in tumor initiation and progression across multiple organ systems. Given the increasing global burden of cancer and rising concerns regarding antimicrobial resistance, understanding the oncogenic roles of bacteria has become essential for guiding prevention and therapeutic strategies. This review provides a novel and integrated perspective by synthesizing mechanistic, microbiome-driven, and cross-cancer evidence on how bacterial pathogens contribute to oncogenesis, while also highlighting the shared microbial patterns observed in both gastrointestinal and extraintestinal cancers such as breast cancer. In this mini-review, we summarize the molecular mechanisms through which oncogenic bacteria facilitate cancer development, discuss microbiome dysbiosis associated with various malignancies, and examine their roles in gastric, colorectal, esophageal, lung, gallbladder, breast, and cervical cancers. Understanding these interconnected pathways may support future development of microbiome-targeted therapeutic interventions and facilitate early detection strategies.