Answer: Kaposi’s sarcoma

Histology: none provided

Discussion: Kaposi’s sarcoma is a controversial entity that represents either a multi-focal reactive process or a true neoplasm. KS has been described in four distinct clinical groups, and in each group, lesions have been shown to have an association with HHV-8. The four clinical groups are as follows: classic (endemic) Kaposi’s sarcoma, AIDS-associated Kaposi’s sarcoma, immunosuppression-associated Kapois’s sarcoma and African Kaposi’s sarcoma. In each group, the histologic appearance may progress from patch to plaque to tumor stage. Patch stage lesions demonstrate a mild increase in dermal vessels that are arranged parallel to the epidermis. Atypia of endothelial cells may be appreciated, and the surrounding dermis contains limited numbers of plasma cells and well as extravasated red blood cells and hemosiderin-laden macrophages. In the plaque stage, the vascular proliferation is more extensive. A proliferation of atypical spindle cells with eosinophilic cytoplasm and hyperchromatic nuclei surrounds the vessels. The current case is an example of the nodular stage, in which the spindle cells predominate. Slit-like vascular channels containing numerous extravasated red cells are noted. The spindle cells are positive for CD34 and variably positive for CD31. The differential diagnosis includes other vascular neoplasms, such as angiosarcoma and kaposiform hemangioendothelioma. Angiosarcoma lacks the spindle cell population of Kaposi’s sarcoma and demonstates a much greater degree of endothelial cell atypia. Kaposiform hemangioendothelioma, a rare entity, usually occurs in infants and children, lacks significant cytologic aytpia and does not contain a prominent inflammatory infiltrate.