Cancer spreads through a process that involves the invasion of blood vessels and lymph nodes near a tumor, according to the American Cancer Society. The ability of cancer to spread successfully depends on a number of factors, and not all cancer cells can metastasize, or spread.
The actual process of metastasis typically involves local invasion of cancer cells into neighboring noncancerous tissue followed by invasion of the cells through the walls of nearby blood and lymph vessels. Cancer cells use the circulatory system to move throughout the bloodstream and the lymphatic system to reach other parts of the body. In the capillaries at a distant location, cancer cells stop moving and invade the walls of surrounding tissues where they begin to multiple to form smaller tumors called micrometastases. New blood vessels form to give these smaller tumors a supply of nutrients and oxygen needed for growth, according to the ACS.
Cancer most commonly spreads to the bones, lungs and liver but can spread to other areas of the body. A few types of metastatic cancer can be cured with the treatments available in 2014, but most are incurable. Most cancer deaths are actually a result of metastatic cancer, according to the ACS.