CD34 Expression in Soft Tissue Tumors: A Comprehensive Guide

In summary, CD34 expression is not specific to any one tumor type and should be interpreted in the context of other clinical and histological features. While it can be helpful in diagnosing certain tumors, such as DFSP and perineuriomas, it's not a reliable marker for all soft tissue tumors. Although 70% to 90% of spindle cell GISTs express CD34, most frequently in rectal and esophageal tumors, at most only 50% of epithelioid GISTs and GISTs of the small intestine are CD34 positive.135 Approximately 20% to 30% of retroperitoneal LMS expresses CD34.171 Diffuse CD34 expression is characteristic of DFSP and can help distinguish this tumor type from benign fibrous histiocytoma/dermatofibroma, which is typically negative for CD34 (although around 5% of benign fibrous histiocytomas may show focal staining). However, when fibrosarcomatous transformation of DFSP occurs, CD34 expression is often lost in the higher-grade component.172,173 CD34 expression is observed in 65% of soft tissue perineuriomas and highlights the delicate cytoplasmic processes of the lesional cells.157 Thus, as endothelial markers, antibodies to CD34 are best used in a panel of reagents designed to account for these other diagnostic possibilities when appropriate. A comprehensive panel of markers should be used to accurately diagnose and differentiate between various soft tissue tumors.