Also known as Gefitinib, ERSA is used to treat patients with EGFR mutation-positive lung adenocarcinoma with a dosage of 250 mg once daily on an empty stomach or with food. If patients cannot swallow the tablets, they can take the tablets dissolved in drinking water without affecting the absorption of the drug. Reactions to ERSA are mild, including skin itching, rash, and diarrhea, and are generally well tolerated by patients. Very few patients may develop interstitial lung disease. If a patient suddenly has difficulty breathing while taking the drug, a chest CT is needed to rule out interstitial lung disease. Nowadays, ERSA has been included in the scope of medical insurance reimbursement and is a regular lung cancer drug.