Tumor is a new organism formed by overgrowth and abnormal differentiation of developing or mature normal cells in human body under the long-term effect of different factors. Unlike normal tissues and cells, it does not grow according to the normal cellular metabolism, but becomes unrestrained and uncontrolled. It grows rapidly and irregularly. It can destroy the structure of normal tissues and organs and affect their functions. Compared with normal cells, tumor cells have abnormal structure, function and metabolism, they have more than normal proliferation ability, and this proliferation is incompatible with the organism. Non-tumorigenic hyperplasia is different from tumorigenic hyperplasia. The former often has obvious stimulating factors, and the hyperplasia is limited to a certain extent and for a certain period of time, once this factor is eliminated, there will be no more hyperplasia, but if it goes beyond a certain limit and qualitative changes occur, it can also become tumorigenic hyperplasia. Malignant tumor cells can also infiltrate and spread to other organs and tissues, and continue to grow exponentially, causing great harm to human body or life. All parts of human body are composed of different cells and tissues. Except for hair, teeth and finger (toe) nails, tumors can occur in almost all organs and tissues and cells. Therefore, tumor is not a simple disease, but a complex disease characterized by the uncontrolled growth of abnormal cells and their spread from the primary site to other sites. Eventually, death results. About 400 kinds of tumors can occur in human body, and people often say that cancer is malignant tumor, which is actually a general term for a large group of diseases.