Immunohistochemical detection of human herpes virus-8 latent nuclear antigen-1 is useful in the diagnosis of Kaposi sarcoma.

Kaposi sarcoma is a low-grade vascular neoplasm that has been shown by molecular analysis to uniformly express the latent nuclear antigen-1 of human herpes virus 8. Differentiating Kaposi sarcoma from other benign or malignant vascular tumors, as well as other nonvascular spindle cell soft-tissue neoplasms, can be challenging. Thus, detection of human herpes virus 8 in fixed tissues would be diagnostically useful. Recently, a monoclonal antibody to human herpes virus 8 latent nuclear antigen-1 has become commercially available for immunohistochemical analysis. We sought to study the sensitivity and specificity of this antibody in the detection of human herpes virus 8 latent nuclear antigen-1 in Kaposi sarcoma. Fixed, paraffin-embedded tissue sections from 21 cases of Kaposi sarcoma, nine cases of spindle cell hemangioma, five cases of cutaneous angiosarcoma, five cases of dermatofibrosarcoma protuberans, one case of vascular transformation of a lymph node, four cases of pilar leiomyoma, four cases of stasis dermatitis, four cases of pyogenic granuloma, and three cases of spindled melanoma were examined immunohistochemically using the rat monoclonal antibody to human herpes virus 8 latent nuclear antigen-1, open reading frame-73 (Advanced Biotechnologies Inc.). Tissue sections were stained with automated immunostainers (Ventana) using heat-induced epitope retrieval and a standard DAB detection kit (Ventana) modified to detect rat Ab. Strong, diffuse, nuclear staining in >10% of tumor cells was considered a positive result. In all, 21/21 cases of Kaposi sarcoma showed strong, diffuse, nuclear staining for human herpes virus 8 latent nuclear antigen-1 (100%), whereas all cases of spindle cell hemangioma, cutaneous angiosarcoma, dermatofibrosarcoma protuberans, vascular transformation of lymph node, pilar leiomyoma, stasis dermatitis, pyogenic granuloma, and spindled melanoma were negative for this antigen. The monoclonal antibody to human herpes virus 8 latent nuclear antigen-1, open reading frame-73, is a highly sensitive and specific marker of human herpes virus 8 infection in paraffin-embedded tissue sections of Kaposi sarcoma. As such, it is an extremely useful tool for differentiating between Kaposi sarcoma and other vascular and nonvascular spindle cell lesions, which do not express human herpes virus 8 latent nuclear antigen-1.