As cancer grows and changes, cells lose their ability to stay in a single tumor mass. When cancer cells get into the lymph system or blood vessel system, they break off. Cells can spread as a single cell or as many tiny cells. The cells circulate until they find a good place to grow. The entire body is supplied by blood and drained by the lymph system.
Metastases can appear in any part of the body.
A site for metastatic cancer must have a blood supply and an environment where it can grow. Cancer cells may travel throughout the body. They only take hold in specific locations. Common sites are the brain, lungs, liver, lymph nodes, bone, skin, and adrenal glands. Some cancers tend to involve the entire body or system from the start.