Cancer is a systemic disease that usually requires systemic treatment, mainly chemotherapy. Like the cycle of chemotherapy, it depends on the pathological stage of the tumor as well as the physical condition of the patient, and the drugs used may also be related. Generally speaking, chemotherapy cycles are more often administered in 3-week intervals, i.e., 3 weeks between 2 chemotherapy sessions, which is a 21-day regimen. Others may require a 28-day regimen, which is a 4-week interval. Some are weekly regimens, such as a single-agent paclitaxel regimen, which may be given once a week. There are also oral chemotherapy drugs, oral Tegretol or Capecitabine that require 2 weeks of medication and then 1 week of rest, which is also a 3-week period. So the cancer chemotherapy cycle also depends on different patients, different conditions.