Premalignant nature of oral lichen planus.

The issue as to whether oral lichen planus is a premalignant disorder is still controversial. This study aimed to examine oral malignancies associated with oral lichen planus and to investigate whether oral lichen planus has an intrinsic malignant potential or whether there are also contributing external risk factors. A retrospective cohort study in 200 Caucasian patients with oral lichen planus was conducted between 1991 and 2003. Aspects such as sex, age, clinical variant, affected anatomical sites, duration of the disease, histopathology, prior immunosuppressive treatment, exposure to potential carcinogens and other concomitant diseases were examined. Histopathological examination was repeated during the follow-up if a malignancy was suspected. Three (1.5%) of the 200 patients developed an oral squamous cell carcinoma at the same site following the initial diagnosis of oral lichen planus after a period of 3-6 years (mean 4.3 years). Contributing external risk factors were also noted in two of the three patients (smoking for 20 years and systemic immunosuppressive treatment for 2 years). The exact incidence of malignant transformation is difficult to establish, because of the low number of patients and because of the possible contribution of external risk factors, which may be relevant in oral malignancy.