1. Departments of Molecular Cancer Science Yamagata University School of Medicine, Yamagata, Japan
2. Oncology Research Center, Research Institute for Advanced Molecular Epidemiology, Yamagata University, Yamagata, Japan
3. Global COE program for Medical Sciences, Japan Society for Promotion of Science, Tokyo, Japan
4. Departments of Neurosurgery, Yamagata University School of Medicine, Yamagata, Japan
5. Department of Neurosurgery, National Cancer Center Hospital, Tokyo, Japan