Response to gefitinib is strongly associated with the status of the epidermal growth factor receptor gene. Here we report the different treatment responses in a case of lung adenocarcinoma coexpressing mutant-type gene in the primary lung mass and a wild-type gene in the metastatic bone lesions. This case demonstrated that at least two strains of tumor cells were present in a single patient. This may be one of the mechanisms of gefitinib resistance.