We reported "Transcription Factor SOX9 Promotes Osteosarcoma Cell Growth by Repressing Claudin-8 Expression" in Tohoku J. Exp. Med., 2017, 241 (1), 55-63; doi: 10.1620/tjem.241.55. After publication of the paper, we have become aware of the ethical violation in collecting the samples from some patients. We therefore wish to retract the paper and apologize for any inconvenience caused by the retraction.