We assessed the usefulness of a mouse monoclonal antibody (13B10) against human herpesvirus 8 (HHV-8) latent nuclear antigen-1 (LNA-1) in diagnosis of Kaposi sarcoma (KS) and for distinguishing it from various mimickers by studying 50 cases of KS and 53 mimickers (angiosarcoma, 15; kaposiform hemangioendothelioma, 6; spindle cell hemangioma, 3; reactive angioendotheliomatosis, 3; bacillary angiomatosis, 4; acroangiomatous dematitis, 2; microvenular hemangioma, 2; hobnail hemangioma, 2; pyogenic granuloma, 5; dermatofibroma, 8; arteriovenous hemangioma, 1; verrucous hemangioma, 1; nonspecific vascular proliferation, 1) from patients with or without acquired HIV infection. Immunohistochemical staining was performed on formalin-fixed, paraffin-embedded tissue sections. All 50 cases of KS were positive for HHV-8 LNA-1, with immunolocalization in the nuclei of the spindle cells and cells lining the primitive and thin-walled vascular channels, whereas all 53 mimickers (including 4 lesions from HIV-positive patients) tested negative. The results idicate that positive immunostaining for HHV-8 LNA- 1 exhibits high sensitivity and specificity for the diagnosis of KS and is, thus, useful for distinguishing it from the mimickers.

Rabbit monoclonal antibody (MAb), which has become available only recently, theoretically combines the advantage of the high affinity attributable to its rabbit origin and the high specificity due to its monoclonal nature. Since immunohistochemical demonstration of cyclin D1 is notoriously difficult, this study aims to assess whether a newly available rabbit MAb against cyclin D1 (SP4) can improve the consistency of immunostaining, especially for the diagnosis of mantle cell lymphoma (MCL). A total of 150 cases of lymphoproliferative lesions, including 30 cases of MCL, histologic mimickers of MCL, and various types of lymphomas and leukemias, were studied. Immunostaining was performed on formalin-fixed, paraffin-embedded tissue sections using a labeled streptavidin-biotin peroxidase system in an automated immunostainer. All cases of MCL expressed cyclin D1, with a higher median staining score (8 out of a maximum of 12) compared with mouse MAb DCS-6 (score 4). In addition, 2 of 15 cases of B-cell chronic lymphocytic leukemia (B-CLL), 3 of 12 cases of multiple myeloma, and 2 of 5 cases of hairy cell leukemia were also positive. Comparable staining results could also be achieved by an optimized manual staining protocol. This study thus confirms the superior performance of the rabbit MAb SP4, which should permit consistent immunostaining for cyclin D1 to be readily achieved. The value of cyclin D1 immunohistochemistry in the differential diagnosis of MCL from other low-grade B-cell lymphomas is also affirmed, but with the caveat that rare cases of B-CLL can also be cyclin D1 positive.

We assessed the usefulness of a mouse monoclonal antibody (13B10) against human herpesvirus 8 (HHV-8) latent nuclear antigen-1 (LNA-1) in diagnosis of Kaposi sarcoma (KS) and for distinguishing it from various mimickers by studying 50 cases of KS and 53 mimickers (angiosarcoma, 15; kaposiform hemangioendothelioma, 6; spindle cell hemangioma, 3; reactive angioendotheliomatosis, 3; bacillary angiomatosis, 4; acroangiomatous dematitis, 2; microvenular hemangioma, 2; hobnail hemangioma, 2; pyogenic granuloma, 5; dermatofibroma, 8; arteriovenous hemangioma, 1; verrucous hemangioma, 1; nonspecific vascular proliferation, 1) from patients with or without acquired HIV infection. Immunohistochemical staining was performed on formalin-fixed, paraffin-embedded tissue sections. All 50 cases of KS were positive for HHV-8 LNA-1, with immunolocalization in the nuclei of the spindle cells and cells lining the primitive and thin-walled vascular channels, whereas all 53 mimickers (including 4 lesions from HIV-positive patients) tested negative. The results idicate that positive immunostaining for HHV-8 LNA- 1 exhibits high sensitivity and specificity for the diagnosis of KS and is, thus, useful for distinguishing it from the mimickers.