What is Metastasis? How Ayurvedic Treatment can help to control Metastasis? What is Metastasis? Metastasis is defined as the spreading of cancer from the primary site or an organ where cancer began to manifest at another site of the body and very common sites are the bones, liver, lungs, and brain. In metastasis, the broken cancer cells of a primary organ, start to travel through the blood or lymphatic system to the other organ and develop a new tumor there.