Most cancer deaths are due to tumour metastasis, a process in which cells break off from the primary tumour, enter the bloodstream, and then enter new tissues where they form secondary tumours. If this occurs in critical organs (e.g. the lungs), it can disrupt organ function and result in death. We have been using microscopy to visualize how tumour cells extend protrusions into the junctions between the cells that make up the blood vessel walls, and then squeeze through the junction so that they can enter the underlying tissue. Interestingly, the movement of tumour cells through the blood vessel wall is greatly increased by the presence of white blood cells. The goal of this proposal is to understand how this occurs. Moreover, since white blood cells accumulate at sites of inflammation, we will test whether inflammation enhances tumour metastasis in mice. If it does, it would suggest that anti-inflammatory drugs might be useful for limiting tumour metastasis.