[Two Cases of Primary Intracranial Solitary Fibrous Tumor:Genetic Examination of <i>NAB2-STAT6</i> Fusion and Its Association with Hemangiopericytoma]

Intracranial anaplastic solitary fibrous tumor/hemangiopericytoma: immunohistochemical markers for definitive diagnosis

Intracranial anaplastic hemangiopericytoma (AHPC) is a rare and malignant subset of solitary fibrous tumor/hemangiopericytoma (SFT/HPC) as per the WHO 2016 Classification of Tumors of the Central Nervous System. AHPC portends a poor prognosis and is associated with higher rates of recurrence/metastasis in comparison with SFT/HPC. Accordingly, it is critical to continue to define the clinical course of patients with AHPC and in so doing further refine clinicopathologic/immunohistochemical (IHC) criteria needed for definitive diagnosis. Herein, we describe clinical/histological characteristics of six patients with AHPC. In addition, we reviewed and analyzed the expression of various IHC markers reported within the literature (i.e., a total of 354 intracranial SFT/HPCs and 460 meningiomas). Histologically, tumors from our six patients were characterized by a staghorn-like vascular pattern, mitotic cells, and strong nuclear atypia. Immunohistochemically, all tumors displayed positive nuclear staining for STAT6; other markers, including CD34 and Bcl-2, were expressed only in three patients. Analysis of IHC expression patterns for SFT/HPC and meningioma within the literature revealed that nuclear expression of STAT6 had the highest specificity (100%) for SFT/HPC, followed by ALDH1 (97.2%) and CD34 (93.6%). Of note, SSTR2A (95.2%) and EMA (85%) displayed a high specificity for meningioma. Anaplastic SFT/HPC is a tumor with poor prognosis that is associated with higher rates of recurrence and metastasis in comparison with SFT/HPC. Given that anaplastic SFT/HPC requires more aggressive treatment than meningioma despite of a similar presentation on imaging, it is crucial to be able to distinguish between these tumors.

Surgical therapy and next-generation sequencing-based genetic alteration analysis of malignant solitary fibrous tumor of the pleura

Background

Solitary fibrous tumor of the pleura (SFTP) is a rare pleural neoplasm arising from mesenchymal cells, accounting for <5% of pleural neoplasms. Approximately 10% of cases of SFTP demonstrate malignant potential, leading to local recurrence after radical surgery and subsequent metastasis.

Methods

A large malignant-like mass was found in the left thoracic cavity of a 61-year-old woman. Following radical resection of the mass, the patient was diagnosed with malignant SFTP by histologic and immunohistochemical analyses. In addition, a next-generation sequencing-based mutation test was used to reveal the mutational profile of the tumor. The genetic alteration panel was analyzed with reference to public data on the ClinVar and COSMIC databases, after which the public SFTP data were analyzed for frequency of altered genes. Finally, through overlay of the abovementioned two sets, the genetic alteration accounting for SFTP initiation was anticipated to be identified.

Results

In the mutation panel of our malignant SFTP group, kinase insert domain receptor (KDR) and fms-related tyrosine kinase 1 (FLT1) scored high in pathogenesis but had only a medium frequency; the NAB2–STAT6 fusion appeared to be the dominant genetic alteration in public SFTP samples.

Conclusion

The high frequency of NAB2–STAT6 fusion indicates its prominent role in SFTP, while somatic mutations such as FLT1-R593W and KDR-V297I may also contribute to the malignant angiogenic phenotype. The present study affirmed the heterogeneity of SFTP, and more sophisticated classification methods will be needed to explore its underlying mechanisms.

Summary

We believe that improvement in the prognosis of SFTP relies on early diagnosis, margin-free resection, and long-term follow-up. Through genetic analysis, it appears that both NAB2–STAT6 fusion and somatic mutations such as FLT1-R593W and KDR-V297I contribute to SFTP development.