Premalignant lesions of the oral mucosa. A discussion about the place of oral intraepithelial neoplasia (OIN).

Oral precancerous lesions are traditionally classified as leukoplakia, erythroplakia, erythroleukoplakia, and distinguished from precancerous conditions. Major attention is focused on leukoplakia, and no distinction made whether dysplasia is or not present. Malignant transformation is a multistep process that should be approached also from the histological, and not merely from the clinical standpoint. Intraepithelial neoplasia, a notion created for the uterine cervix and already extended to other mucosae, should be adapted to the oral mucosa and used as diagnostic term. OIN (oral intraepithelial neoplasia) is not only a change in terminology, but also a progress in the unifying concept of precursors of squamous cell carcinoma, suppressing the useless discussion between severe dysplasia and carcinoma in situ. Furthermore, grading lesions as low or high grade OIN increases diagnostic consistency. OIN is suspected on three clinical patterns reflecting histological changes: mosaic, irregular keratosis, erythroplakia (or intermediate aspects), but dysplastic mucosa may also appear normal clinically.