Cancer cells can be carried in the bloodstream or lymphatic system to other parts of the body. There they can start to grow into new tumours. The diagram shows a primary bowel cancer that has spread to the liver.In order to spread, some cells from the primary cancer must break away, travel to another part of the body and start growing there. Cancer cells don’t stick together as well as normal cells do. They may also produce substances that stimulate them to move.
The diagram shows a tumour appearing in cells lining a body structure such as the bowel wall. The tumour grows through the layer holding the cells in place (the basement membrane). Some cells can then go into small lymph vessels or blood vessels called capillaries in the area.