The "intraepidermal epithelioma" revisited: immunohistochemical study of the borst-jadassohn phenomenon.

The true nature of the so-called intraepidermal epithelioma of Borst-Jadassohn is poorly understood; whether this represents a distinct tumor or a morphological phenomenon [Borst-Jadassohn phenomenon (BJP)] shared by different entities has been debated. So far, no detailed immunohistochemical studies have been performed to address this issue. The aim of our study was to get further insight into the pathogenesis of the intraepidermal epithelioma of Borst-Jadassohn/BJP. Tumors showing the BJP [mainly clonal seborrheic keratoses (cSK) and clonal Bowen disease (cBD)] were studied and compared with typical (nonclonal) counterparts. Cell nests in cSK, cBD, hidroacanthoma simplex (HS), and porocarcinoma (PC) showed strong expression of epidermal growth factor-receptors (EGF-R), Ki-67, p63, and p53. Cell nests of clonal SK and HS (but not of clonal BD or PC) expressed keratin 5/6. The expression of E-cadherin and the number of CD1a+ Langerhans cells were reduced within the nests of all lesions, whereas melanocytes were increased in all of them. Keratins 7 and 19 were not expressed in any of the lesions. Tumors showing the BJP exhibit some immunohistochemical differences, suggesting that they represent separate entities. However, they all show strong expression of EGF-R within intraepidermal keratinocyte nests, suggesting that the epithelial growth factor pathway plays a role in the development of the BJP.