Footnotes

• YL and QY contributed equally.

• Contributors YL, QY, CR, XD, AH and CL contributed to the development and submission of this manuscript as follows: designing the study, directing its implementation and writing the discussion section; pathological review and immunohistochemical study; experiments on HPV status and genotype; conducting the literature review; preparing the materials and methods and case study sections; supervising the entire research activities and revising it critically for important intellectual content.

• Funding National Natural Science Foundation of China (grant no. 81472430).

• Competing interests None.

• Patient consent Obtained.

• Provenance and peer review Not commissioned; externally peer reviewed.