During the clinic, I often encounter patients who ask: Will my glioma metastasize? The author will patiently answer: Glioma will not metastasize outside the brain! The main reason is that the environment outside the body is not suitable for glioma growth. In other words, there is a big difference between the environment inside the brain and the environment of lung and liver. If tumor cells are the seeds and organs are the soil, then glioma cells, the seed, can only grow if they are planted in the brain. However, in the study, it was found that if a certain number of glioma cells were planted under the skin of nude mice, they could also form tumors under the skin of nude mice. This suggests that immune mechanisms play a large role in the development of gliomas. Since there is a natural barrier between the brain and the blood, the immune function in the brain is much weaker than in the body (jargon refers to the brain as the “immune special immune organ”. In addition, the glioma cells planted under the skin of nude mice in the experiment need to be of a certain order of magnitude to become tumors, whereas in the natural human environment, assuming that the glioma cells stay in an organ such as the lung or liver with the blood, their number is extremely low, which is one of the reasons why they cannot become tumors outside the brain. It should be said that multiple factors contribute to the inability of glioma to metastasize outside the brain. Not all brain tumors cannot metastasize outside the brain. The literature reports that malignant meningioma can metastasize to organs such as the lungs. As mentioned before, the brain is an immune special immune organ, and the immunity in the brain is much weaker than that in the body; therefore, tumors in the body will grow more rapidly when they metastasize to the brain. In male patients, it is most common for lung cancer to metastasize to the brain, and in female patients, it is most common for breast cancer to metastasize to the brain. We found that almost all malignant tumors in the torso can metastasize to the brain. There are also tumors that can occur both in the brain and in the body. For example, malignant lymphoma can occur in both the body and the brain due to the presence of lymphocytes in both. In short, malignant tumors in the body can basically metastasize to the brain, while malignant tumors in the brain cannot basically metastasize to sites outside the brain. The most common malignant tumor in the brain is glioma.