Squamous cell carcinoma arising in lichen planus on the buccal mucosa.

Lichen planus is considered to be a precancerous condition, and in the west, it is not rare for cases of lichen planus in the mucosa of the lips or oral cavity to become malignant in comparison with such lesions occurring in the skin. Among the cases of lichen planus of the oral mucosa in Japan, there are very few which have become malignant. In oral surgery, no cases have been reported such as the present one where lesions of lichen planus were diagnosed to be cancerous in the initial histopathological examination and then the focus of the same lichen planus, shifted into cancerated lesions in the same institution, thereby confirming malignant changes.The present case was a 63-year-old man with erosive lichen planus in the bilateral buccal mucosa. The synthetic retinoid preparation etretinate was administered orally, but the symptoms did not improve, and the left buccal lesion where a biopsy was performed 6 months after the first examination was found to have developed into squamous cell carcinoma. The cancerous lesion was cured by administration of peplomycin and radiotherapy. At present, 5 years and 6 months after irradiation, its development course including the right lesion has made satisfactory progress.