1. Department of Histology and Embryology, Binzhou Medical University, Yantai, Shandong 264003, P.R. China
2. Department of Surgery, Yantai Shan Hospital, Yantai, Shandong 264003, P.R. China
3. Department of Radiotherapy, Yantai Shan Hospital, Yantai, Shandong 264003, P.R. China