Due to the lack of fundamental metabolic differences between tumor cells and normal cells, all anticancer drugs cannot completely avoid damage to normal tissues. Moreover, the therapeutic index (i.e., the relationship between therapeutic benefit and toxicity) of most chemotherapeutic drugs is relatively small, so the treatment must strictly grasp the indications, choose the best dose, control toxic side effects and avoid life-threatening toxic side effects. These adverse reactions appear early and mostly occur in proliferating tissues, such as bone marrow, gastrointestinal tract, hair follicles, etc. I. Bone marrow suppression The half-life of various hematopoietic cells in bone marrow determines whether their cell count is reduced or not. Most bone marrow stem cells are normally in resting phase and enter the mitotic pool only after chemotherapeutic agents have damaged mature cells. The stem cell pool can deliver mature blood cells to the peripheral blood within 8-10 days after damage by cytotoxic drugs. In previously untreated individuals, a decrease in WBCs and Pt is seen on day 9 or 10 after the first dose of chemotherapy without CSFs, reaching a nadir on days 14-18 and recovering significantly by day 21. The above pattern can change due to the following factors: depletion of the stem cell pool, earlier onset of WBC and Pt reduction, and longer recovery time. the duration of WBC and Pt decline to the nadir is most clinically significant. The risk of infection and bleeding is greatest when WBC<500/dl and Pt<10×109. If the nadir lasts only 4-7 days, most patients can tolerate it without supportive therapy. Most antineoplastic drugs do not damage the bone marrow by increasing the dose within the maximum tolerated dose range, even without prolonging the recovery time, but affect their nadir levels. Re-administration during early bone marrow recovery (day 16-21) can cause severe bone marrow toxicity in the second cycle of chemotherapy in tumors of non-marrow origin or in those with uninvolved bone marrow. Gastrointestinal reactions Most chemotherapeutic drugs can cause gastrointestinal reactions such as nausea and vomiting, especially in platinum-containing chemotherapy regimens. Oral mucositis and diarrhea are mostly seen with antimetabolites. Therefore, most anticancer drugs can cause hair loss in varying degrees, including cyclophosphamide, vincristine (VCR), adriamycin (ADM), bleomycin (BLM), and onychomycin (VP-16). However, hair can regrow after stopping chemotherapy. Ice cap in chemotherapy can reduce hair loss. Local irritation Some chemotherapeutic drugs can stimulate local veins to produce phlebitis when injected intravenously, such as 5-Fu, vincristine (NVB). V. Allergic reactions BLM can sometimes cause allergic reactions, causing chills, high fever, shock, and even death in patients. Some protein agents such as menadione are also prone to cause allergic reactions. The botanical drug VP-16 is a large-molecule drug, and rapid sedation can also cause laryngeal edema and spasm, deficiency and other allergic reactions. Special organ toxicity involves the kidney, liver, heart, lung, central nervous system and gonads. 1. Renal tubular necrosis Cisplatin can cause tubular necrosis if used without proper hydration and diuretics to maintain large urine volumes. Similarly, high doses of methotrexate (MTX) can be deposited in the renal tubules, especially when the urine is acidic or highly concentrated. Hydration, alkalinization of the urine with sodium bicarbonate and the use of diuretics can prevent renal damage. When using such drugs inosine clearance should be tested regularly. 2. Hepatotoxicity Hepatotoxicity can occasionally occur with the use of L-ASP or extended use of methotrexate (MTX) or 6-mercaptopurine (6- MP). Rarely, liver damage can occur even with therapeutic doses. Cardiotoxicity Cardiotoxicity is mainly seen with anthracycline anticancer agents such as adriamycin and erythromycin, but also with high-dose cyclophosphamide therapy. It can be sudden, reversible but with high mortality. Transient ECG changes, or delayed myocardial damage and congestive heart failure, can occur at cumulative doses of adriamycin above 550 mg/m2 or above 450 mg/m2 in the setting of concurrent radiotherapy. Autopsy reveals myocardial cell breakdown and interstitial edema. Caution is needed when using anthracycline anticancer agents when the patient has a history of cardiac disease, especially when the cardiac region is treated with radiotherapy, or in combination with cyclophosphamide, as both drugs can cause myocardial lesions. Early detection of myocardial toxicity by regular monitoring of left heart ejection fraction is necessary to avoid serious and irreversible consequences. Routine electrocardiogram examination before chemotherapy and electrocardiogram monitoring during chemotherapy are required. 4. Pulmonary toxicity Mainly seen with bleomycin (BLM) as BLM is selectively deposited in the lungs. When total BLM accumulation exceeds 400 IU or a single dose exceeds 30 IU, clinically significant pulmonary fibrosis occurs in approximately 5% of patients presenting with decreased pulmonary diffusion function and total lung function. Clinical manifestations are unexplained cough, shortness of breath, and fine reticular and nodular shadowing in the diaphragmatic angle of both ribs on a dry umbrella x-ray of the lung base. Regular pulmonary examination during drug administration, the occurrence of pulmonary toxicity should be immediately discontinued, and active symptomatic treatment. Leucovorin and mitomycin (MMC) may occasionally produce pulmonary toxicity. 5, neurotoxicity Most commonly seen in vincristine (VCR), which is characterized by peripheral neuropathy, manifested by loss of deep tendon reflexes, abnormal sensation, motor weakness, and occasionally pain in the jaw or other areas. Such changes may recover after several months. Cisplatin and paclitaxel neurotoxicity is also characterized by peripheral neuropathy. About 31% of those using cisplatin can develop ototoxicity, manifested by tinnitus or/and deafness in the high frequency region. Methylbenzhydrazine and levomepromazine can cause central nervous system symptoms, including drowsiness, hallucinations, and depression. The use of methotrexate after whole brain radiation therapy can increase the concentration of drugs in brain tissue to produce brain white matter necrosis leading to cerebral leukomalacia. Some drugs can cause gonadal damage and infertility, including various alkylating agents, vincristine, methylbenzylhydrazine, cytarabine, and cisplatin. Combination chemotherapy, such as the MOPP regimen for Hodgkin's disease, can cause gonadal damage in more than 80% of male patients, as evidenced by azoospermia, testicular atrophy, and elevated gonadotropin levels. Ovarian failure can occur in female patients after chemotherapy, especially in women with breast cancer over the age of 40 years who often suffer from amenorrhea after combination chemotherapy. 7. Second primary tumors The occurrence of second primary tumors is gaining attention due to the increase of patients in long-term remission and cure. Because most anticancer drugs are mutagenic, the results of follow-up after combination chemotherapy for Hodgkin's disease are as follows: (1) chemotherapy alone or chemotherapy plus radiotherapy is more likely to cause acute leukemia than radiotherapy alone; (2) the peak incidence of acute leukemia occurs 3-9 years after the end of chemotherapy, followed by a decline in incidence; (3) the incidence of acute leukemia is most often seen with alkylating agents, methylbenzylhydrazine and nitrosourea, suggesting that this complication can be reduced by changing the This suggests that this complication can be reduced by changing the chemotherapy regimen. The risk of second leukemia increases with age at the time of primary tumor treatment, especially in those older than 40 years.