After gefitinib resistance, it is better to carry out genetic testing, so as not to delay the follow-up treatment. Gefitinib is a kind of targeted drug for treating lung cancer, and the target point is mainly EGFR mutation, although the side effects are relatively small, but it has a certain degree of drug resistance, so it is necessary to carry out genetic testing in time, and it is important to know that after the drug resistance of this kind of drug, the lung cancer tissues may have new gene mutations, such as ROS as well as ALK, and so on. If the genetic testing is not done properly at this time, then the treatment effect will be drastically reduced, and the disease cannot be effectively controlled and may progress, affecting the prognosis. Therefore, patients should pay special attention to the process of treatment, do not blindly take drugs, but under the guidance of the doctor. Once gefitinib resistance occurs, then it is necessary to carry out genetic testing in a timely manner, and to change the appropriate drug according to the actual situation.