Altered patterns of keratin expression in oral hairy leukoplakia: prognostic implications.

To establish why the lateral border of tongue is the site of predilection for the development of hairy leukoplakia (HL) and to understand its likely behavior, the pattern of keratin expression was compared in 8HL lesions with matched controls in an immunocytochemical study. Keratins 7, 8, 18 were absent in HL and normals; uniform basal keratin 19 was present in normals but much reduced in HL. Loss of conformationally sensitive epitopes of keratin 14 in lower epithelial layers was seen in HL. Overall expression of non-cornifying keratins 4/13 was reduced in HL and completely lost in the parakeratin zone. Expression of the high-turnover keratins 6/16 was reduced in HL. The HL keratin phenotype suggests that no dysplastic change is likely, but in contrast there is enhanced differentiation, which suggests a benign course for the condition.