Cancer cells have the ability to “metastasize”. Normal cell membranes have a kind of “glycoprotein”, which can enhance the adhesion between cells and cells and between cells and the surrounding matrix, so that the cells are not easily loosened and shed. However, the shortage of “glycoprotein glycoconjugates” in cancer cell membranes reduces the adhesion between cancer cells and between cancer cells and the surrounding matrix, which makes cancer cells easily shed and move around. When cancer cells stay in another place, take root and multiply, “metastatic cancer” is formed. Blood metastasis is a common way for cancer cells to metastasize. Cancer cells invade blood vessels, enter the bloodstream, break off from the walls of blood vessels, run with the blood, and then choose to stay in a certain blood vessel. Large blood vessels often cannot stop because of the fast flow rate. The place where they can stop must have a very slow blood flow rate and be particularly rich in capillaries. After the cancer cells stop, they penetrate the walls of blood vessels and reach new organs or new tissues, where they continue to multiply and establish new territories, forming metastases. In human body, liver has many capillary sinuses; lung and brain are also rich in blood flow; bone, especially where cartilage meets or bone marrow cavity has many capillaries. These places above are rich in blood flow and slow in blood flow, which are ideal destinations for cancer cells to stop, and therefore are prone to liver metastasis, lung metastasis, brain metastasis and bone metastasis. Cardiac metastasis rarely occurs because it is difficult for cancer cells to stop because of the fast blood flow in the heart. Many people have a misconception that early stage cancer will not metastasize. In fact, what we mean by early stage is “clinical early stage”, that is, the early stage determined by using imaging tests such as ultrasound, CT or MRI. However, some small metastases cannot be detected by these examinations. Therefore, there may be micro-metastases in early clinical stage of cancer, but they are not detected by imaging. Lung, kidney and prostate cancers tend to have early blood metastases. In breast cancer, early blood metastasis is equally important as lymphatic metastasis. When the cancer cells have entered the bloodstream before surgery and are in the blood circulation, it cannot be cured simply by open surgery at this time, which is the blood residue and will cause recurrence after surgery. It should be noted that the cancer cells that run into the blood do not always form metastases. A considerable number of cancer patients, through examination, are found to have cancer cells in the blood, but some of them do not develop metastatic foci, but are on the way to metastasis.