Core Insights - Tumor-infiltrating bacteria, particularly Fusobacterium nucleatum, are increasingly recognized as key components of the tumor microenvironment (TME) and are linked to cancer recurrence and treatment resistance [2][5] - The recent study published in Cancer Cell highlights a new mechanism by which these bacteria disrupt interactions between cancer epithelial cells and induce cell-cycle arrest, leading to resistance against chemotherapy drug 5-fluorouracil (5-FU) [3][10] Summary by Sections Tumor-Infiltrating Bacteria and Cancer - Tumor-infiltrating bacteria, especially in mucosal sites, are being viewed as critical elements of TME [2] - Specific bacteria have been associated with cancer progression and poor prognosis, such as the enrichment of Fusobacterium nucleatum in colorectal cancer (CRC) tissues [2] Mechanism of Action - The study describes how extracellular bacteria, including Fusobacterium nucleatum, regulate the behavior of cancer epithelial cells [6] - These bacteria are primarily found in the extracellular regions of the TME in colorectal and oral cancers, where cell density, transcriptional activity, and proliferation are reduced [6] Experimental Findings - In vitro experiments show that Fusobacterium nucleatum disrupts epithelial cell contact, causing cells to enter a G0-G1 phase and inhibiting transcriptional activity [6] - This state confers resistance to the chemotherapy drug 5-FU and remodels the tumor microenvironment [6] - The findings were validated through live-cell imaging, spatial analysis, mouse models, and a cohort of 52 colorectal cancer patients [6] Clinical Implications - High loads of Fusobacterium nucleatum in tumors correlate with reduced treatment response [8] - The study emphasizes the potential of targeting microbial-tumor interactions as a therapeutic strategy [10]