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Unlabelled: The purpose of this work was to study the value of HHV8 latent nuclear antigen 1 detection by immunohistochemistry in Kaposi sarcoma and its mimics., Materials and Methods: : We used the mAB LNA53 against the latent nuclear antigen 1 of HHV8 to study its expression by immunohistochemistry in paraffin embedded biopsy of Kaposi and its mimics. We also performed in vitro PCR for HHV8 DNA, extracted from the same paraffin embedded biopsies. We studied characteristic lesions of 26 Kaposi sarcoma; 20 cutaneous lesions raising problems of differential diagnosis. We also studied 11 biopsies of skin, mucosa, or lymph nodes of patients infected by HHV8 but without Kaposi sarcoma, and 22 lesions initially classified by histological analysis as uncertain Kaposi sarcoma ., Results: : In all cases of Kaposi, HHV8 was detected in the majority of tumor cells, with no expression in other adjacent cells. In these biopsies HHV8 DNA, was identified by in vitro PCR. None of the 20 Kaposi sarcoma mimics and the 11 lesions of patients infected by HHV8 but without any Kaposi sarcoma, were HHV8+ on immunohistochemistry sections or by PCR. From the 22 cases of uncertain Kaposi sarcoma, only the 14 lesions HHV8 PCR+ and with a clinical evolution in accordance with a Kaposi sarcoma, were HHV8+ on immunohistochemistry. In contrast, the 8 cases negative for HHV8 on immunohistochemistry were also PCR- and had a self-healing evolution in accordance with the diagnostic of pyogenic granuloma., Conclusion: : Detection of the latent nuclear antigen 1 of HHV8 by immunohistochemistry is a specific and sensitive diagnostic tool for differentiating Kaposi sarcoma from its mimics.