How are malignant solitary fibrous tumors (SFTs) of the pleura diagnosed?

Updated: Dec 25, 2019
  • Author: Joseph F Tomashefski, Jr, MD; more...
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The features used to diagnose malignant SFT are those of England et al. [9] A high labeling index for Ki-67 and positive staining for p53 have been reported more frequently in malignant than in benign SFTs. [61] No difference has been shown in various histopathologic features or in Ki-67 or p53 staining in extrapleural versus pleural SFTs. [61]

Negative staining for pankeratin and positive staining for CD34 are useful in differentiating SFT from sarcomatoid mesothelioma. Focal keratin positivity in a histologically typical SFT likely represents entrapped mesothelial cells or lung epithelial cells. [3] However, rare CK-positive, CD34-negative malignant SFTs have been described. [10] Distinction from extraintestinal GIST can be readily determined by lack of staining of SFT for CD117 (in most cases). [74] CD34 is nondiscriminatory in this regard, since 47%-100% of GISTs showed positive staining for CD34. [3]

Panels of markers, including CD34 and keratin, are also helpful in distinguishing SFT from other spindle cell mesenchymal neoplasms. Distinction of malignant SFT from monophasic synovial sarcoma may prove challenging, especially in SFTs that lack CD34 expression or exhibit cytokeratin staining. FISH analysis for SYT rearrangement has been shown to be uniformly negative in SFTs and can be diagnostically helpful in this situation. [10]

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