Malignant potential of oral lichen planus; a follow-up study of 326 patients.

326 patients with oral lichen planus were followed for periods ranging from 6 months to 10 years (mean 4.8 years), in an attempt to clarify the malignant potential of this disease which is still controversial. Malignant transformation occurred in 4 patients (1.3%) in a mean time of 6.5 years after the onset of lichen planus. Before cancer development, 3 of these patients manifested the erosive form of oral lichen planus, while the others, a combination of the papular/atrophic form. Malignant transformation in our patients could not be associated with any evident factors, such as family history, local irritation, alcohol consumption, nutritional disturbances or other systemic diseases.