The decision of when chemotherapy is needed depends on a combination of factors such as the pathological nature of the disease, stage, and the patient’s physical condition. Take lung cancer as an example, if it is early stage lung cancer, there is no lymph node metastasis after surgery and the stage is stage I, postoperative adjuvant chemotherapy can be unnecessary. For stage II or above, including stage II, stage III and stage IV, chemotherapy is required. The same is true for breast cancer. Stage I can be treated without chemotherapy, while stage II, III and IV all require chemotherapy. There are cases such as leukemia, lymphoma and other hematologic diseases where chemotherapy is the main treatment, and only through chemotherapy can these diseases reach a curative situation, regardless of the stage one that requires chemotherapy.