The same bacteria present in primary tumors of patients with colorectal cancer are also present in liver metastases, a new study finds. What's more, presence of the bacteria was found to correlate with tumor growth. Previous studies have found an abundance of Fusobacterium nucleatum in human colon cancers. To explore whether colon cancer that has spread to other parts of the body also harbors the bacteria, Susan Bullman et al. analyzed samples of primary tumors and corresponding liver metastases in colon cancer patients. They not only confirmed the presence of Fusobacterium in the metastases, but found that the strains were highly similar to those found in primary tumors of the same individual. Notably, patients who did not have Fusobacterium within their primary tumors also lacked the bacteria in their metastases. When the researchers transplanted Fusobacterium-positive tumors into mice, the tumors took hold, whereas tumors lacking the bacteria did not. Lastly, antibiotic treatment of mice with Fusobacterium-positive tumors reduced the amount of Fusobacterium in the tumors and slowed tumor growth. Based on these results, the authors speculate that Fusobacterium travels with metastatic tumor cells to distant organs, perhaps aiding their colonization at these sites.