Suprabasal 40 kd keratin (K19) expression as an immunohistologic marker of premalignancy in oral epithelium.

The authors have studied the expression of keratin 19 in normal oral mucosa and in oral lesions exhibiting a range of histopathologic changes that are thought to precede squamous cell carcinoma. Formalin-fixed, paraffin-embedded sections were pretreated with pronase and stained with a K19-specific antibody by the avidin-biotin immunoperoxidase method. In nonkeratinized mucosa, whether normal or benign hyperplastic, K19 was detectable in the basal cell layer. In keratinized mucosa, whether normal or benign hyperplastic, there was no detectable K19. All lesions from any oral site that exhibited atypia diagnosed from hematoxylin and eosin stained sections as moderate-to-severe dysplasia or carcinoma in situ, whether hyperkeratotic or not, stained strongly for K19 in the basal and suprabasal cell layers. The number of cell layers that were K19-positive correlated with the level in the epithelium to which dysplasia persisted. Suprabasal K19 staining tended to occur in regions of the epithelium in which expression of the terminal differentiation protein involucrin was delayed or absent. Thus, K19 expression may be linked to the retention of stem cell character or a state otherwise uncommitted to terminal squamous differentiation. Suprabasal K19 staining is clearly correlated with premalignant change in oral epithelium and therefore promises to be a useful tool in oral histopathologic diagnosis.