The chemotherapy cycle may exceed 21 days. Chemotherapy refers to the use of chemotherapeutic drugs to kill cancer cells to achieve the therapeutic purpose, is an important means of treatment of malignant tumors, clinically most patients are treated in accordance with a cycle of 2-4 weeks, and most chemotherapy is a cycle of 21 days because it takes time for chemotherapeutic drugs to exert their therapeutic effect and expose the adverse reactions, and the body needs time to adapt to and repair the chemotherapeutic drugs that cause damage. Not all patients are 21 days, for example, for patients with postoperative adjuvant chemotherapy for colon cancer, there exists a regimen of 14 days as a cycle, and there are also some patients whose chemotherapy cycle will exceed 21 days. The cycle and course of chemotherapy need to be determined according to the patient’s condition and specific drugs. It is suggested that patients who need chemotherapy should be actively treated under the guidance of doctors so as not to delay their condition.