Clinical History
This 50-year-old patient was found to have in incidental dural based mass. What is your diagnosis?
Correct Answer
The H&E stained sections demonstrate a cellular proliferation of relatively monotonous appearing spindle to ovoid cells with patchy “staghorn” type vascular pattern. Frequent mitotic figures (>20/10hpf) were present. STAT6 immunostain shows diffuse strong staining of the neoplastic cell nuclei.
The overall features are consistent with the diagnosis of a dural-based solitary fibrous tumor / SFT. This lesion was previously designated as hemangiopericytoma / HPC).
The STAT6 overexpression in the neoplastic cells is driven by the presence of NAB2::STAT6 gene fusion due to genomic inversion at 12q13. This is an excellent example of an immunostain being used to impute a genetic abnormality (i.e. surrogate marker for molecular testing).
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