Cancer microbiota: a focus on tumor-resident bacteria

Accumulating evidence highlights the presence of an intratumoral microbiota across various cancer types. Among all the microorganisms comprising the tumor-associated microbiota, tumor-resident bacteria (TRB) are increasingly recognized as critical regulators of cancer biology. Within tumor tissues, these microorganisms interact with various components of the tumor microenvironment (TME) and influence both tumor-promoting and tumor-suppressing pathways, underlying their dual role in cancer. Fully understanding the functional roles of TRB and their complex interactions with components of the TME requires the application of multimodal technologies. Developing strategies to modulate TRB-either by eradicating pathogenic populations or harnessing beneficial ones-holds great promise for advancing cancer treatment. In this review, we summarize the most recent insights into TRB. We discuss their possible origins and their implications on cancer biology, focusing on their roles in cancer development, metastasis establishment, immune modulation, and therapy response. Finally, we describe bacteria-based strategies and address the major challenges in detecting and analyzing these microbial communities in tumors.