Cancer thrombus is caused by cancer. In clinic, cancerous thrombus is formed when malignant tumor cells invade into lymphatic vessels and blood vessels, resulting in the coalescence of cancerous cells in blood vessels, and this kind of thrombus is mainly composed of cancerous cells, so cancerous thrombus is not the same as ordinary thrombus, and it is caused by cancer. Usually, the presence of a cancerous thrombus means that the malignant tumor in the body has metastasized. When a patient develops a cancerous thrombus, it may cause localized edema or pain, which is mainly caused by the blockage of blood vessels by the cancerous thrombus, resulting in poor blood circulation in the body, and the patient should actively carry out treatment to control the development of the disease. Cancer patients should seek timely medical treatment when they feel unwell to avoid aggravation of the disease.