Cancer is the second leading cause of death in the United States, as reported in a 2010 report by the Centers for Disease Control and prevention. Researchers have identified a main component to cancer related fatality is not the primary tumor but secondary tumor metastases. Circulating tumor cells (CTC) have been identified as important prognostic markers of secondary tumor metastasis. CTCs have been identified in both early and late stages of cancer diagnosis, but are not currently completely understood. Successful isolation and characterization of CTCs from cancer patients will increase understanding of the mechanisms of cancer dissemination. The discovery of critical molecules specific for CTCs will provide targets for molecular guided therapy.