Chemotherapy is a common anti-tumor treatment. Chemotherapy may shrink the tumor, but the number of times of chemotherapy is uncertain, there may be effect after 1 or 2 times of chemotherapy, for example, lymphoma is very sensitive to chemotherapy, it may shrink the tumor after 1 time of chemotherapy. However, there are some tumors that are not sensitive to chemotherapy and several times of chemotherapy can only prevent further development and growth, but not shrink the tumor. For example, in the case of pancreatic cancer, the use of gemcitabine-based chemotherapy regimen may be able to control the disease and hardly shrink the tumor through chemotherapy. Some chemotherapy is used as preoperative neoadjuvant chemotherapy, if it can shrink the tumor and reduce the stage, there is still a chance of surgical cure later. As preoperative neoadjuvant chemotherapy, it usually needs to be applied for 4-8 courses, and the efficacy needs to be reviewed and evaluated after every 4 courses.