Swollen lymph nodes are often the earliest signs of spread of cancer cells. Swedish researchers have now discovered how cancer cells can infiltrate the lymphatic system by disguising themselves as immune cells (white blood cells). The main reason why people die of cancer is that the cancer cells spread to form daughter tumours or metastases in vital organs such as the lungs and liver. A route frequently used by cancer cells for dissemination is the lymphatic system. Upon entering lymphatic vessels they migrate to nearby lymph nodes which then swell up and from there to other organs via the blood.