Metastasis means cancer spreads to a special part from where it started. When this happens, doctors say cancer has “metastasized.” Your doctor can also call it "metastatic cancer," "advanced cancer," or "stage 4 cancer." But these terms can have different meanings. For example, cancer that's large but has not spread to a different part also can be called advanced cancer or locally advanced cancer. Ask your doctor to explain where cancer has spread. Metastases is the plural form of metastasis. Metastases most ordinarily develop when cancer cells break free from the most tumor and enter the bloodstream or systema lymphaticum. These systems carry fluids around the body. This means that the cancer cells can travel far away from the first tumor and form new tumors once they settle and grow during a different part of the body. Metastases also can sometimes develop when cancer cells from the most tumor, typically within the belly, or abdomen, break off and grow in nearby areas, like within the liver, lungs, or bones.