Keratin 10-positive orthokeratotic dysplasia: a new leucoplakia-type precancerous entity of the oral mucosa.

AIMS: We investigated a group of oral mucosal lesions with characteristic hyperorthokeratotic foci, which we termed orthokeratotic dysplasia (OKD), to determine if it could be identified as a distinct histopathological entity.

METHODS AND RESULTS: We screened 282 surgical specimens from 200 patients with oral leucoplakia-type squamous cell carcinoma (SCC) or carcinoma in situ (CIS). OKD was defined as an oral mucosal lesional focus in which hyperorthokeratosis was predominant in the presence of the granular cell layer. A total of 84 OKD foci from 62 cases found among the 200 SCC/CIS cases were analysed. According to its rete ridge shapes, OKD was classified into three subtypes: flat (14.3%), leg (63.1%) and intermediate (22.6%). Eighty per cent of OKD foci were adjacent to the main foci of SCC or CIS, and they were demarcated sharply from each other. Most of the OKD constituent cells were immunopositive for keratin 10, but not for keratins 13, 17 or 19. Numbers of Ki-67-positive cells in the first basal layer were greater in OKD than in normal epithelia.

CONCLUSIONS: The findings indicate that OKD is a distinct variant of epithelial dysplasia related to malignancies, and hence that it is important to recognize its existence.