[Retracted] Upregulation of the δ opioid receptor in liver cancer promotes liver cancer progression both and .

Following the publication of the above paper, it was drawn to the Editor's attention by a concerned reader that the western blotting data shown in Fig. 1C on p. 1284 for the control β‑actin protein bands were strikingly similar to bands appearing in another article written by different authors at different research institutes, which had already been submitted for consideration for publication (Li ZH, Yu Y, Du C, Fu H, Wang J and Tian Y: RNA interference‑mediated USP22 gene silencing promotes human brain glioma apoptosis and induces cell cycle arrest. Oncol Lett 5: 1290‑1294, 2013). Owing to the fact that the contentious data in the above article had already been submitted for publication elsewhere prior to its submission to , the Editor has decided that this paper should be retracted from the Journal. After having been in contact with the authors, they agreed with the decision to retract the paper. The Editor apologizes to the readership for any inconvenience caused. [International Journal of Oncology 43: 1281‑1290, 2013; DOI: 10.3892/ijo.2013.2046].