We explain this with the example of mutations in the EGFR gene, the most common driver gene in lung cancer patients. First, not all mutation types can be restrained by existing targeted drugs, and studies have only confirmed that some of these “sensitive mutations” (e.g., exon 19 deletion mutations and exon 21 point mutations) are treated with targeted drugs. If a patient carries a type of gene variant that is not sensitive to the targeted drug, it is likely that the drug will be ineffective. Secondly, most patients usually develop “drug resistance” after taking EGFR targeted drugs for a period of time (9-14 months on average), resulting in treatment failure. Therefore, it is important to follow up with your doctor regularly during targeted therapy to detect resistance and take countermeasures.