Correspondence to: Dr. ZHANG Zhen-fa, Department of Lung Cancer, Lung Cancer Center, Tianjin Medical University Cancer Institute & Hospital, National Clinical Research Center of Cancer, Key Laboratory of Cancer Prevention and Therapy, Tianjin 300060, China (Tel: 86-22-23340123 ext. 3184. Fax: 86-22-83718833. Email: zhangzhenfa1973 @ 163.com)