Overestimated risk of transformation in oral lichen planus.

<bold>Objectives: </bold>Oral lichen planus (OLP) was classified as an oral potentially malignant disorder due to the association with oral squamous cell carcinoma (OSCC). However, the malignant potential of OLP has been controversial. Whether epithelial dysplasia should be differentiated from OLP and lichenoid dysplasia could be identified as a pathological entity has been the subject of debate.<bold>Materials and Methods: </bold>We recruited a large retrospective cohort with 3568 patients, and 10 of them developed OSCC. These cases were reviewed retrospectively to investigate association between OLP and OSCC.<bold>Results: </bold>In 10 cases of OSCC, three of them were primary cancers distinct from the site with OLP, two were malignant transformation of proliferative verrucous leukoplakia, and five were malignant transformation of oral leukoplakia. All OSCC is not transformed from OLP. Therefore, previous insights into OLP might have overestimated its transformation risk. There may be the reasons: I. did not distinguish OLP from epithelial dysplasia, II. neglect of oral leukoplakia with dysplasia developed in the course after OLP, III. misdiagnosis in the early stage of proliferative verrucous leukoplakia.<bold>Conclusion: </bold>The pathological and molecular biological features of OLP differed from those of oral leukoplakia and OSCC. Strict control of the diagnostic criteria for OLP and close surveillance during the course could contribute to correctly identify the origin of OSCC and avoid overestimating the risk of OLP transformation. [ABSTRACT FROM AUTHOR]