In clinical practice, we can often encounter such a phenomenon: the tumor cells are more sensitive to the drugs during the first chemotherapy for malignant tumors, and the tumor volume shrinks quickly after chemotherapy. However, once the residual tumor increases in size, the effect of using the same chemotherapeutic drugs again will be reduced, and even the development of tumor cannot be controlled. At this time, it suggests that the tumor cells are resistant to the anti-cancer drugs. There are multiple mechanisms for the development of drug resistance, such as reduced uptake of anti-cancer drugs by cells. Therefore, at this time, if the maximum diameter of the tumor increases by 25%, tumor progression is considered and the chemotherapy regimen needs to be changed. Local radiotherapy can also be considered, as radiation can have a very good effect on local tumor elimination. For example, TKIs for lung cancer are often resistant in 3-6 months, and can be replaced by chemotherapy regimens. The latest research has confirmed that most patients will be effective again with 2-4 cycles of chemotherapy after TKIs resistance. This can improve patient survival and quality of life.