Genetic testing is a must before using targeted drugs, without which targeted drugs cannot be used. Because the main target of targeted drugs is a certain gene mutation in tumor, the use of corresponding targeted drugs for this gene mutation can achieve the purpose of “one key to open one lock” and better control the growth of the disease. Take lung cancer as an example, before targeted drug therapy, genetic tests such as EGFR gene mutation, ALK mutation or HER2 overexpression must be done to guide the use of targeted drugs such as gefitinib, crizotinib and trastuzumab. The presence of the appropriate genetic mutation is required for the use of targeted drugs to have significant clinical efficacy. Current studies have shown that the use of targeted drugs is more effective than chemotherapy or radiation therapy if there is a genetic mutation. If there is no genetic mutation, the use of targeted drugs is ineffective, so the appropriate genetic testing must be done before targeted drug therapy is administered. Each tumor is tested for different genes; lung cancer has a genetic test for lung cancer, while rectal cancer or breast cancer has a different genetic test.