Cancer metastasis is the process where cancer cells spread from the primary tumor to distant sites in the body. There are 5 major steps in metastasis: 1) invasion of surrounding tissue, 2) release into circulation, 3) survival in circulation, 4) arrest in capillaries of distant organs, 5) penetration of vessel walls and growth. Metastasis can occur through the bloodstream (hematogenous), lymphatic system, or body cavities. Cancer cells degrade the extracellular matrix using enzymes to migrate, and can die from detachment, damage in vessels, or immune system attack. Some cancers have preferential metastatic sites thought to be due to anatomical proximity or a compatible tissue environment.