Metastasis is the medical term for cancer that spreads to a different part of the body from where it started. When this happens, doctors say the cancer has "metastasised." Other names for metastasis are "metastatic cancer" and "stage 4 cancer." Sometimes the term "advanced cancer" also describes metastatic disease. Metastases most commonly develop when cancer cells break away from the main tumor and enter the bloodstream or lymphatic system. These systems carry fluids around the body. This means that the cancer cells can travel far from the original tumor and form new tumors when they settle and grow in a different part of the body.