We report the clinical and pathological findings of two cases of Bowen's disease (BD) with features resembling myrmecia wart, and tried to find evidence of human papillomavirus (HPV) infection in such lesions by immunohistological staining, genotyping systems, polymerase chain reaction (PCR) and electron microscopy. Both cases manifested unique barnacle-like hyperkeratotic nodules or plaques clinically, and microscopically proliferation of atypical keratinocytes involving the entire thickness of the epidermis, hypergranulosis with eosinophilic and/or basophilic inclusion bodies, features that mimicked myrmecia wart. Electron microscopy revealed myrmecia inclusion-like large intranuclear and cytoplasmic electron-dense bodies. Immunohistological staining with anti-HPV antibody, genotyping systems for HPV infection and specific PCR designed to detect HPV-1 L1 sequences failed to detect evidence of HPV infection. P16INK4a was overexpressed in the atypical keratinocytes of both cases. This finding suggests that the pathogenesis of these two BD may involve certain unknown or undetectable HPV, or reflect disturbances of the Rb signaling pathway unrelated to HPV infection. The unique "myrmecioid" clinicopathological features in our cases suggest that this type of lesion may be a new variant of BD.
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