Differential Diagnosis of Meningeal SFT-HPC and Meningioma Which Immunohistochemical Markers Should Be Used?

Meningeal solitary fibrous tumors-hemangiopericytomas (SFT-HPC) and meningiomas can be difficult to distinguish on histologic examination. STAT6 immunohistochemistry (IHC) is a reliable diagnostic marker of SFT-HPCs. Recently, GRIA2 has also been reported to be a diagnostic marker of SFT-HPC, although no extensive data are available for meningeal SFT-HPCs yet. The aim of this study was to test their diagnostic performance in a large cohort of SFT-HPCs and meningiomas. IHC analyses for GRIA2 and STAT6 were performed on tissue microarrays containing 76 SFT-HPCs and 181 meningiomas. Results were compared with previous data with ALDH1 and CD34. Two different anti-STAT6 antibodies were tested: SC-20 polyclonal and YE361 monoclonal antibody. Ninety-six percent of meningeal SFT-HPCs but no meningioma displayed nuclear STAT6 positivity. With SC-20 antibody, concomitant cytoplasmic staining for STAT6 was observed in > 50% of all cases, including meningiomas. However, using YE361 antibody, cytoplasmic staining was absent, and nuclear signal intensity was stronger leading to better interpretation of STAT6 IHC. GRIA2 was positive in 84% of SFT-HPCs and in 16% of meningiomas. STAT6 had excellent sensitivity (96%) and specificity (100%), ALDH1 and GRIA2 had same sensitivity (84%), but ALDH1 and CD34 had better specificity than GRIA2 (97% and 96% vs. 84%, respectively). For the differential diagnosis of SFT-HPCs versus meningiomas, the best diagnostic approach is to perform STAT6, followed by ALDH1 and CD34 in the case of uncommon STAT6-negative cases. Because of meningioma positivity, GRIA2 seems less useful in this indication.