Chemotherapy is a kind of systemic treatment, and the application of dexamethasone tablets before chemotherapy is mainly to prevent allergy and vomiting. Because chemotherapy is a kind of treatment with more side effects, the most important reactions are nausea, vomiting, and may also cause allergic reactions, such as rashes all over the body, etc. At this time, the application of oral dexamethasone tablets can prevent allergic reactions, and can also reduce the vomiting reaction. Commonly used drugs such as docetaxel and paclitaxel need to take dexamethasone tablets before use, and some antiemetic drugs can also be used intravenously, such as ondansetron intravenously. After chemotherapy also need to regularly review the blood routine, liver function, kidney function and other tests, may cause white blood cell drop, platelet reduction and other side effects, also need to be treated symptomatically.