Expression of CD34-antigen in nasopharyngeal angiofibromas.

Formalin-fixed, paraffin-embedded and frozen tissues of 24 patients with primary nasopharyngeal angiofibroma, of whom seven had recurrences, were studied immunohistochemically for the expression of CD34 antigen using two different antibodies (HPCA-1 and QBEND 10). In all cases, there was an exclusive staining of endothelial cells, while pericytes, smooth muscle cells and stromal fibroblasts were not reactive. The staining intensity, however, was more pronounced in small tumor vessels of capillary- and sinusoidal-type than in larger vessels, which were usually characterized by an irregular smooth muscle coat. This differential staining indicates an increased proliferative potential of the endothelium of the small vessel component of nasopharyngeal angiofibroma (neoangiogenesis) and an inhibitory influence of vascular smooth muscle cells on endothelial cell growth. Moreover, the positive immunoreaction of all endothelial cells for CD34 is indicative of the absence of lymphatic vessels, which confirms previous ultrastructural observations. No differences in the staining pattern were observed between primary versus recurrent tumors, formalin fixed, paraffin embedded versus snap-frozen acetone fixed material, or between both CD34 antibodies. Our findings indicate that nasopharyngeal angiofibroma is a vasoproliferative malformation.