CD34: A Marker for Vascular Differentiation in Soft Tissue Tumors

CD34, the hematopoietic progenitor cell antigen, is recognized by several monoclonal antibodies including My10/HPCA1, QBEND-10, and BI-3C5.165,166 CD34 is a 110-kD transmembrane glycoprotein expressed by embryonic cells of the hematopoietic system,167 including both lymphoid and myeloid cells and endothelial cells. Correspondingly, again in the setting of soft tissue tumors, CD34 is a potential indicator of vascular differentiation. It is a relatively sensitive marker for the endothelial lineage and recognizes more than 85% of angiosarcomas and Kaposi sarcomas.165,166 However, in the authors' experience, reactivity for CD34 is observed in only approximately 60% of poorly differentiated angiosarcomas, which limits its diagnostic utility in this setting. Moreover, the specificity of CD34 is low, inasmuch as CD34 expression is seen in some LMS, PNSTs, and epithelioid sarcomas,167-169 which could potentially simulate variants of angiosarcoma or hemangioendothelioma. In addition, CD34 is so commonly detected in DFSP and its variants and in spindle cell lipoma, GIST, and solitary fibrous tumor that it is regularly used as an adjunct to the diagnosis of these tumor types. Overall, CD34 is a useful marker for identifying vascular differentiation in soft tissue tumors, particularly in angiosarcomas and Kaposi sarcomas. However, its limited sensitivity and specificity in poorly differentiated angiosarcomas and its expression in other tumor types must be taken into consideration when interpreting results.