Footnotes

• Contributors WT-T collected the clinical data and wrote the manuscript. H-YH collected the clinical data. W-CT provided the pathological interpretation and critically revised the manuscript. K-H K critically revised the manuscript.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

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