1, recent toxic reactions: CTX and other high-dose shock therapy in the use of 3-4 days after the decline in white blood cells, 6-7 days back up, which is the recent toxic effects on the hematopoietic system. 2.Mid-term toxic reactions: such as methotrexate and vincristine, etc., the leukocyte decline starts in 10-14 days of drug administration, and the rebound starts in 20 days. 3. Delayed toxic reactions: The decrease in white blood cells occurs after 3 weeks of drug use and starts to rise in 4-6 weeks. The severity of the drug’s effect on the hematopoietic system is closely related to the type of drug and the dose level. For those who have damage to the hematopoietic system, the time of leukocyte decline is often significantly shortened, and the time of rebound is mostly 12-14 days after the lowest point of leukocyte decline. The paclitaxel drugs commonly used in breast cancer chemotherapy have a greater effect on bone marrow suppression, and granulocyte-stimulating factor support therapy is often routinely administered 24-48 hours after chemotherapy. Other chemotherapy regimens like FEC, AC, NP, GP, etc. without paclitaxel do not routinely raise leukocytes. In fact, it is important to strengthen the routine blood tests, which can usually be repeated 3, 5, 7, 11 days after chemotherapy.