Hi doctor, my father is diagnosed with ca. Lung - adeno carcinoma with egfr mutation stage 4 advanced with plural effusion as origin. He had severe cough and also fluid formation in left lung which almost half filled the left lung. The fluid is removed by surgery and then further tests are carried out. Ct, histopathology, ihc, and gene analysis were done. Medical oncologist suggested afatinib 40 mg and it is working fine since 3 years as his gene analysis showed above 90% mutation that can be controlled by gefitinib and only 3% comprises of t790m which may not work and develop resistance later. Last week pet scan shown no signs of tumor, however cea continue to be above 24-26 over last 6 months. However, afatinib 40 mg is too expensive drug and to continue using and has become problematic for the family to support using this medicine. Can we can switch to erlotinib 150 mg or gefitinib instead of afatinib? Will this give same results now as afatinib? What are the risks involved? Please advise alternatives that are cost effective.