SOD1 and squamous cell intraepithelial neoplasia: The CTC group has a significantly lower level of SOD compared with the CTL, CTC.CVSL, CTC.CV, and CTC.SIL groups, whereas there was no statistical difference between the CTL group and the CVSL, CTC.CVSH, CTC.CVSL, CTC.CV, and CTC.SIL groups.