Which immunohistochemistry findings are characteristic of malignant solitary fibrous tumors (SFTs) of the pleura?

Updated: Dec 25, 2019
  • Author: Joseph F Tomashefski, Jr, MD; more...
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SFTs nearly always express the immunohistochemical markers vimentin and CD34, with slightly less frequent expression of Bcl-2 and CD99. [71, 72] Rare tumors may coexpress desmin or actin. Mesothelial markers such as calretinin are negative, as are epithelial markers such as pankeratin and EMA. [3, 8, 9] However, the mesothelial marker D2-40 is occasionally positive in the spindle cells of SFT. [73] CD117 is usually negative. [74] Endothelial markers such as CD31 and Factor VIII are negative in tumor spindle cells but highlight intra-tumoral vascular endothelial cells.

CD34, while not specific, is perhaps the most useful marker for supporting the diagnosis of SFT. Staining for CD34 and Bcl-2, however, may be weak or absent in malignant SFTs. [8] Rare malignant SFTs with expression of cytokeratin have also been described. [10]

The nuclear proliferation marker Ki67 (MIB-1) may be useful in discriminating benign from malignant SFTs, with benign lesions having a low proliferative index (0%-2%), while frankly malignant lesions show 20%-40% nuclear positivity. In one large series, the mean proliferative index for benign tumors was 7.27 versus 13.48 for malignant SFTs. [61] P53 has also been advocated as a useful marker seen in a higher proportion of malignant than benign SFTs. [10, 61, 72]

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