The immunohistochemical detection of endothelial differentiation in skin tumors has been hindered by the relative paucity of reliable markers that are applicable to rou- tinely-processed specimens, which are both specific and sensitive as well.

This study was designed to evaluate the utility of CD31 and CD34, newly introduced vascular markers, in the immunohistochemical differentiation of vascular neoplasms from other mesenchymal tumors and to compare their sensitivity and specificity with factor VII-related antigen (FVIIIRA).

Paraffin-embedded specimens of 26 cases of benign and malignant vascular tumors and 25 cases of non-vascular mesenchymal neoplasms of the skin and subcutis were investigated for CD31, CD34, and FVIIIRA expression using immunohistochemical methods.

CD31-immunoreactivity was observed in all of the 26 vascular lesions. CD34 and FVlllRA were labelled in 23 cases and 16 cases of vascular tumors, respectively. All of the 25 non-vascular mesenchymal tumors were negative for CD31 and FVIIIRA. In contrast, positive reactivity for CD34 was seen in 14 cases, among which dermatofibrosarcoma protuberans(2/2), neurofibroma(8/8), neuriilemmoma(2/2), and leiomyoma(2/3) were included.

Our results indicate that CD31 is a more sensitive and specific vascular marker than CD34 and FVIIIRA. A small panel composed of these three antibodies will constitute a comprehensive and reliable method for identifying tumors of vascular origin.