The term secondary cancer is used to describe the spread of a cancerous growth away from the site where it originally developed. For example the primary site of the cancer could be in the gut with malignant cells spreading from the gut to form a secondary cancer in the liver. Different tumours have a propensity for spreading to particular tissues such as prostate cancer tending to spread to bone. Cancers can spread by various means. They may invade the surrounding healthy tissue thereby increasing in size. A typical example of this is the rodent ulcer on the face eroding into the surrounding skin. Cancerous cells may also spread through the blood and lymphatic system, which can convey cancer cells well away from their site of origin. An example of this would be the spread of lung cancer cells to the brain. Secondary cancer implies a poorer prognosis because the growth has spread beyond the initial boundaries that contained it.