Metastatic disease, also known as metastasis, is the spread of cancer cells from the original tumor to other parts of the body. This is a complex process involving the migration of cancer cells through the bloodstream or lymphatic system to distant organs or tissues, where they can form new tumors. Metastatic disease is a serious complication of cancer and is responsible for the majority of cancer-related deaths. Research in this area focuses on understanding the underlying mechanisms of metastasis, developing new treatments to target metastatic cancer cells, and finding ways to prevent or delay the spread of cancer.