Interestingly, our present results were in line with observation by Yanase et al (2004) showing that when gefitinib-sensitive A431 lung cancer cells were transduced with BCRP (A431/BCRP) they became markedly resistant to gefitinib whereas BCRP transfection in gefitinib-insensitive leukemic K562 (K562/BCRP) and P388 (P388/BCRP) cells did not much further increase gefitinib resistance. The gene discussed is ABCG2; the disease is lung carcinoma.