Ultrastructural Localization of CD34 in Soft Tissue Tumors

Abstract The CD34 antigen is a single chain, heavily glycosylated transmembrane protein originally identified in hematopoietic stem cells. Subsequently it was found to be expressed in cells of normal endothelium and a variety of soft tissue tumors, including: epithelioid sarcoma, solitary fibrous tumor,’ gastrointestinal stromal tumor and dermatofibrosarcoma protuberans. Using paraffin immunohistochemistry, membranous and cytoplasmic staining for CD34 can be seen in these lesions, with most showing a combination of both. The findings of cytoplasmic staining is unexpected, as CD34 is a transmembrane cell surface protein. We analyzed the ultrastructural localization of CD34 on two soft tissue tumors with membranous and combined membranous and cytoplasmic staining. Biopsy specimens were fixed with a mixture of 4% paraformaldehyde and 1% glutaraldehyde in 0.1M sodium cacodylate buffer, pH = 7.4 for 1-2 hours, and embedded in Poly/Bed 812 with osmium tetroxide post-fixation, or in LR White without osmication. The immunogold method was performed on ultrathin sections placed on Nickel grids,