Spread is one of the characteristics of malignant tumor. Its ways are: 1. Direct spread: while the tumor volume gradually increases, the tumor cells can extend directly along the weakness of surrounding normal tissues (medically called tissue gap), invade and destroy the neighboring tissues or organs, this process is called direct spread by doctors. For example, rectal cancer can spread to prostate, bladder (male), uterus and vaginal wall (female), etc. 2.Plantation spread: When tumors located in organs in the body cavity (such as lung cancer, stomach cancer, ovarian cancer, etc.) infiltrate to the external surface of organs (medically called plasma membrane surface), with corresponding friction such as breathing or intestinal peristalsis, some of the shed tumor cells can grow and multiply in other parts of the body cavity to form new lesions. This kind of diffusion is called implantation dissemination. Liu Xijun, Department of Radiotherapy, Shandong Institute of Cancer Control and Prevention 3. Metastasis: Metastasis refers to the process of tumor cells running from the primary place to other places to grow and multiply, and the formed tumor is called metastatic tumor. Metastasis occurs through two pathways: lymphatic tract and blood tract. Tumor cells can metastasize to lymph nodes when they invade lymphatic tract, and blood tract metastasis occurs when they invade into blood vessels. Once cancer cells invade lymphatic vessels, they can be shed and form emboli or proliferate and form continuous masses in the vessels, but most of them enter regional lymph nodes through lymphatic vessels and form intra-lymph node metastasis. Generally the earlier the lymph node metastasis appears, the more extensive it may also be. Bloodstream metastasis may occur when lymphatic fluid containing cancer cells enters the bloodstream (along the thoracic duct), or when cancer cells directly invade small blood vessels. Cancer cells that enter the bloodstream move through the bloodstream as individual cells or as a mass connected by fibrin. Cancer cells that normally enter the blood circulation do not survive, but when they get a chance to stay in the course of their run, they invade out of the duct wall and enter the interstitium around the blood vessels and grow into metastases. Anticoagulants and chemotherapy have the potential to reduce tumor metastasis, while compression and local manipulation may increase the chance of metastasis. Different tissues of the organism have different affinities for metastasis. Liver, lung, bone marrow, brain and adrenal gland are the common sites of metastasis, while spleen and muscle rarely show metastasis. Generally, blood metastasis occurs in the later stages of the disease, but blood metastasis can occur in the early stages of lung, breast, kidney, prostate and thyroid cancers.