Colorectal cancer is responsible for a substantial proportion of cancer-related deaths worldwide.

Increasing evidence suggests that the gut microbiome has a role in the development and progression of colorectal cancer. In addition, it has been shown that solid tumours host various bacteria, and the functional roles of those in cancer development are beginning to be uncovered. In this study, He et al. show that Campylobacter jejuni is enriched in the primary tumours from patients with metastatic colorectal cancer and that a bacteria-derived genotoxin named cytolethal distending toxin (CDT) promotes metastasis.