Metastatic Cancer: How Cancer Spreads

According to the National Cancer Institute, metastasis usually has several steps. First, the invasive malignant cells penetrate tissue near the site where the cancer started growing; by this time, the first tumor has stopped growing. From there, the cancer cells continue to move until they reach a blood vessel or lymph vessel. Lymph vessels are often compared to veins in the circulatory system, but instead of transporting blood, lymph vessels help collect and move waste material as part of the immune system. The cells that reach a vessel may travel through the body in the bloodstream or the lymph system. The cells will eventually stop in smaller blood vessels and work their way out. Once in their new location, the cells may multiply into small tumors that will prompt new blood vessels to form; these blood vessels supply the cancer cells blood for continued growth. Screenings for certain cancers, including breast and prostate cancer, are especially important for identifying a cancerous tumor before it has the opportunity to spread.