Primary and secondary cancers. Artwork showing the spread of cancer from a primary site in the skin (upper left), through the blood stream (centre), to form secondary cancers elsewhere in the body (right). The secondary locations shown here are the lungs, liver and a skeletal long bone. The body will produce white blood cells (orange spheres) to attack the cancer cells (purple), but once the cancer has spread (a process called metastasis), the prognosis is poor. Secondary and primary cancers can be treated by surgery and/or radiotherapy and chemotherapy, depending on the location of the tumours.