1. Department of Cancer Epidemiology, National Cancer Center, Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, PR China
2. Department of Pathology, National Cancer Center, Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, PR China
3. National Office for Maternal and Child Health Surveillance of China, West China Second University Hospital, Sichuan University, Chengdu, PR China