Quorum sensing peptides are small protein-like compounds, which are used by certain bacteria to communicate with each other. However, this phenomenon is not limited to the bacteria themselves: recent research demonstrates that these compounds interact with human cells as well. As such, these particular compounds potentially can explain the role of bacteria in/on our body in health and disease. Several quorum sensing peptides have recently been shown by us to influence the behavior of colorectal cancer cells: they stimulate colon cancer cell invasion and angiogenesis, processes that are linked to tumor metastasis. Building on these findings, we will investigate if, under which conditions and at what levels these quorum sensing peptides are present in biological media (blood, stool), and if they indeed cause colorectal cancer metastases in mice, whether or not after production by different bacterial species and strains.