Oral squamous cell carcinoma arising in a patient with long-standing lichen planus. A case report. The risk of malignant transformation of oral lichen planus remains a controversial point. Many previous reports have been discounted on the basis of inadequate information or lack of histologic confirmation of lichen planus. We report a well-documented case of long-standing cutaneous and oral lichen planus in which squamous cell carcinoma of the dorsal portion of the tongue occurred. There is an apparent difference in the sites of oral carcinomas in patients with lichen planus compared with the general population. This suggests that lichen planus increases the risk of oral cancer in affected sites. 