Chemotherapy refers to the use of chemotherapeutic drugs to kill cancer cells so as to achieve the purpose of treatment. Chemotherapy drugs can reach most organs and tissues in the body with the body’s blood circulation, so it is suitable for patients with tumors that have the tendency to spread throughout the body, as well as patients with mid- to late-stage tumors that have metastasized. When patients undergo chemotherapy, some toxic side effects may occur. Therefore, chemotherapy is not suitable for everyone and has certain contraindications, such as poor physical condition, severe bone marrow suppression, pregnancy or lactation. Some of the more common clinical contraindications to chemotherapy are as follows: 1. Poor physical condition: Before chemotherapy, doctors usually score the patient’s physical activity status, or PS, to understand the patient’s health status and ability to tolerate treatment. Patients with a PS score of more than 3 cannot undergo chemotherapy, because such patients are usually in too poor a physical condition or cannot take care of themselves and need to be bedridden for a long time, and cannot tolerate chemotherapy. 2. Severe myelosuppressed patients: Patients often have myelosuppression after chemotherapy, which is manifested by peripheral blood leukopenia and thrombocytopenia. In general, chemotherapy cannot be continued when the peripheral blood leukocyte count is less than 2×10^9/L, or (and) platelet count is less than 50×10^9/L, or when there is severe anemia; 3. Those with other serious combined diseases: for example, combined with serious heart or kidney diseases, or with sepsis, severe respiratory tract infection, urinary tract infection, and very short expected survival are not suitable for chemotherapy. Because most chemotherapy drugs have strong toxic side effects, such patients may be aggravated or even die after chemotherapy; 4. Those who are allergic to chemotherapy drugs: Many chemotherapy drugs can induce lethal allergic reactions, such as paclitaxel and rituximab. If a patient has ever had an allergic reaction during the use of such drugs, it is generally prohibited to use such drugs again for chemotherapy; 5. Pregnant or breastfeeding women: It is prohibited to receive chemotherapy before terminating pregnancy or stopping breastfeeding. Because most chemotherapy drugs can be secreted through breast milk, thus affecting the health of the baby, and may also lead to serious consequences such as malformation and stillbirth. Therefore, chemotherapy is not recommended for those who have one or more of the above conditions, otherwise it can cause serious adverse effects.