At present, most tumor patients do not know much about why they need chemotherapy and how to view the effects and side effects of chemotherapy. So much so that some patients are reluctant or even refuse to receive regular and effective chemotherapy because they are afraid of certain side effects of chemotherapy drugs, such as nausea, vomiting, white blood cell drop, hair loss, etc., resulting in losing their precious treatment time. So, why do malignant tumor patients need chemotherapy? One, chemotherapy can effectively kill tumor cells, inhibit tumor growth, and even cure some tumors. In fact, tumor cells are metabolizing every moment like normal cells, that is, newborn cells replace dead cells. However, the fundamental difference between tumors and normal tissues is that the number of new cells and the number of dead cells in normal tissues are basically equal; whereas the number of new cells in tumors is much more than the number of dead cells, so tumors will grow bigger and bigger. Most chemotherapeutic drugs are used to kill tumor cells by inhibiting or blocking the process of cell division and proliferation (i.e. neonatal process), but of course, they inevitably have some effect on normal tissue cells. Generally speaking, the faster the growth and the higher the malignancy of the tumor, the better the efficacy of chemotherapy drug treatment. Chemotherapy can kill the tumor cells remaining after surgery or radiation therapy, thus enhancing the effect of surgery or radiation therapy. For early solid tumors, surgery should be preferred. However, because the etiology of tumor is not yet clear and there is a lack of effective and specific means for early diagnosis, once tumor patients are diagnosed, most of them are already in the middle or late stage and lose the time for surgery. Even if some of them can be removed surgically, they cannot be cured. They must be treated with chemotherapy to eliminate the residual tumor tissue in order to improve the survival time and quality of life. Third, chemotherapy can prevent or delay the recurrence or metastasis of tumor. It is found that for 1 cm diameter tumor tissue (about the size of peanut rice) in human body, about hundreds of tumor cells are shed into blood and lymphatic circulation every day, and in the early stage, the body can recognize and kill these tumor cells through immune system without metastasis to other organs. When the immune function of the body is low and the tumor is large, the tumor cells that enter the blood circulation may cause metastasis to other organs. Therefore, tumor is actually a systemic disease. Surgical treatment can only remove the local tumor lesions, but can do nothing to the potential metastatic lesions. Chemotherapy can not only destroy the local residual tumor lesions after surgery, but also inhibit or kill the tiny metastatic lesions existing in other organs of the body. In conclusion, chemotherapy is one of the main treatment means for malignant tumors. If tumor patients can carry out regular, reasonable and timely chemotherapy and other treatments under the guidance of tumor specialists, they can not only achieve good chemotherapy effects, but also avoid or reduce the adverse reactions caused by chemotherapy. This is very beneficial to improve the cure rate, prolong the survival time and improve the quality of life of tumor patients.