In the treatment of malignant tumors, systemic chemotherapy (referred to as chemotherapy) can successfully shrink and eliminate the tumor mass, or even cure the disease, but it can also damage the normal cells of human body and bring about adverse reactions such as vomiting, hair loss, and leukocyte drop, etc. Therefore, how long chemotherapy should be used depends on three factors: the nature of the tumor, the physical condition of the patient, and therapeutic drugs. For certain tumors with fast cell proliferation, such as certain highly malignant lymphoma, small cell lung cancer, testicular seminoma, choriocarcinoma and so on. These tumors grow rapidly, are sensitive to drugs, and can be easily “completely destroyed” by chemotherapy, which is characterized by “advancement without retreat”. Chemotherapy is the main treatment means for these tumors, and it is necessary to “get rid of all the evils” at the beginning of the treatment; if it is stopped in the middle of the treatment so that the tumors can come back, it will often induce the tumor’s resistance to drugs, and then it will be difficult to control them completely. Therefore, the principle of treatment should be “no treatment is to, treatment must be sufficient”, in the case of physical conditions allow, must be given enough consolidation chemotherapy, and strive for a cure. Contrary to the above situation, the cell proliferation of another type of tumor is not fast and not sensitive to chemotherapy. For example, hepatocellular carcinoma and renal clear cell carcinoma. At present, the existing chemotherapeutic drugs often have little effect on this kind of tumors, and even if the dose is increased and the time is prolonged, it is feared that the toxicity will be increased more than the therapeutic efficacy, which will add to the pain and economic burden in vain. Therefore, the principle of chemotherapy should be “alleviate pain and stop at the point”, i.e. chemotherapy is often used to suppress the tumor when it progresses wildly and alleviate the pain of the patients, but not a means to strive for a complete cure. Chemotherapy is seldom used alone for this kind of tumor, but combined with targeted therapy and immunotherapy to achieve the best effect. Then, for most other tumors between the above two, such as non-small cell lung cancer, breast cancer, gastric cancer, esophageal cancer, colorectal cancer and other digestive tract tumors, and ovarian cancer and other reproductive system tumors, what kind of chemotherapy is the most reasonable? At this time, the situation is more complicated, and it should be “appropriate according to the tumor”. First of all, if the patient has been operated and the main tumor has been removed, the role of drugs is to remove the scattered tumor cells that may remain in the body, and the chemotherapy at this time is called “adjuvant chemotherapy”. The duration of postoperative medication should not be extended indefinitely, but should have a reasonable time limit to ensure that it is “basic insurance” for the patient and does not cause unnecessary pain. Through a long time, a large number of cases, experience and lessons learned, people have roughly found out some rules, such as non-small cell lung cancer can be treated with 4-6 cycles of chemotherapy after operation, ovarian cancer needs to be treated with more than ten cycles of chemotherapy, etc. However, this is not set in stone. However, this is not invariable, if the patient’s physical condition is poor, it is necessary to shorten the time and reduce the medication appropriately; on the contrary, if the tumor has “high risk factors”, such as high degree of malignancy, late clinical staging, rapid growth of the tumor, etc., then it is necessary to add more cycles of chemotherapy. The “high risk factors” of various tumors are not the same, but have some commonalities, and timely detection and correct assessment of them is one of the essence of the art of chemotherapy. With the development of science and technology, some “markers” that can indicate tumor recurrence and metastasis at an early stage have been discovered, and dynamic observation of these markers can also help to assess the risk of recurrence and decide whether to stop or continue chemotherapy. In addition, more sophisticated imaging methods such as PET-CT can help to detect small metastases or residual lesions at an earlier stage. For tumors that recur after surgery, metastasize, or cannot be removed at the time of diagnosis, chemotherapy is often used to shrink and stabilize the tumor for long-term maintenance. This is called “palliative chemotherapy”. As a matter of fact, it is difficult to stipulate the time of palliative chemotherapy, because this kind of chemotherapy will be carried out in “human-tumor coexistence”, and the purpose is to inhibit (not eliminate) the tumor for a long period of time, so as to make the tumor and the human body in a balanced and stable state. Therefore, its general principle should be “suppressing tumor development, maintaining long-term stability, and ensuring quality of life”, i.e., actively treating the tumor when it develops, reducing the amount of chemotherapy when it is stable, and postponing or even suspending chemotherapy. So, is it true that “life goes on, chemotherapy goes on”? This is not the case. Especially with the emergence of new drugs such as gene-targeted therapy and anti-angiogenic agents with unique anti-tumor effects and less toxic side effects, the therapeutic effects of liver cancer, lung cancer, gastrointestinal cancer and other tumors have been greatly improved, and the modern treatment is increasingly developing into the mode of suppressing the rapid growth of tumors with chemotherapy, and maintaining the long-term stability of tumors with new drugs, so as to “use fast drugs quickly and slow drugs slowly”, complement each other’s advantages, and achieve the goal of “life never stops, chemotherapy never stops”. In this way, “fast drugs are used quickly, slow drugs are used slowly”, complement each other’s advantages, and obtain the greatest anti-tumor effect, the smallest toxic side effects and the best quality of life. As for the question of “how long chemotherapy should be given”, it should be different from person to person, from disease to disease, and from drug to drug, and no generalization can be made.