Final answer:
Metastasis is the process where cancer cells travel through the blood and lymphatic vessels to form new tumors, called metastases, in other tissues.
Step-by-step explanation:
Cancer spreads from the primary tumor to other parts of the body using the bloodstream or the lymphatic system, leading to the establishment of new tumors called metastases. This can occur at various sites in the body, with common areas being the brain, lungs, bones, and liver. Metastasis is a hallmark of the progression of many cancers and represents a significant challenge in cancer treatment because it often leads to a poor prognosis.