For example, gefitinib (Gef) is a standard treatment for the NSCLC patients harboring the EGFR L858R mutation, but over 60% of the patients receiving Gef therapy would develop secondary mutation T790M (threonine substituted by methionine at amino acid position 790) and cause drug resistance 4. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.