Solitary Fibrous Tumors in Pediatric Patients: A Rare and Potentially Overdiagnosed Neoplasm, Confirmed by STAT6 Immunohistochemistry

Abstract

Pathological diagnosis of solitary fibrous tumor (SFT) in the pediatric population is challenging, as it occurs uncommonly in this age-group and resembles other spindle cell neoplasms. SFT contains a NAB2-STAT6 fusion gene, which can be reliably detected using STAT6 immunohistochemistry. Positive staining is highly sensitive and specific. We sought to investigate the utility of STAT6 immunohistochemistry, to show how commonly SFT was historically recognized at 3 academic pediatric institutions, to reclassify them when appropriate, and to demonstrate features of major mimics of SFT. Our series included cases with a previous diagnosis of SFT or for which SFT was among key considerations, from 3 major academic pediatric hospitals seen over the past 30 years. Of 18 tumors identified, only 3 tumors from 2 patients demonstrated positive STAT6 staining as well as the typical histology and immunophenotype seen in SFT. The remaining 15 tumors were reclassified based on morphology, additional immunohistochemistry and fluorescence in situ hybridization as desmoid-type fibromatosis (3 tumors), nerve sheath/neural tumors (3 tumors), low-grade fibromyxoid sarcoma, medallion-like dermal fibroma, poorly differentiated Sertoli cell tumor, nodular/proliferative fasciitis, calcifying fibrous tumor, aneurysmal bone cyst of soft tissue, STAT6-negative SFT with adipocytic differentiation, undifferentiated small round blue cell tumor, and scar (1 tumor each). Our study confirms that SFT is rare in the pediatric population and that it is potentially overdiagnosed. STAT6 immunohistochemistry is recommended to confirm the diagnosis of SFT in the pediatric population.

Solitary Fibrous Tumor of the Umbilical Region in a Pediatric Patient

“…6 Tan et al examined 30 years of archives from 3 pediatric hospitals and identified 18 solitary fibrous tumor diagnoses. 9 Of the 18 tumors, only 3 tumors from 2 patients demonstrated positive STAT6 staining and the typical histology and immunophenotype of solitary fibrous tumors. The remaining 15 tumors were reclassified as other types of soft tissue tumors after application of STAT6 immunohistochemistry, highlighting the rarity of solitary fibrous tumors in children and the importance of STAT6 as the diagnostic marker.…”

“…5 Solitary fibrous tumors have been reported to show immunoreactivity for CD34, Bcl-2, and CD99. 9 The discovery of gene fusion between NAB2 and STAT6 that leads to the upregulation of STAT6, a novel immunohistochemical marker, has been shown to be of diagnostic importance in these tumors. 6 Tan et al examined 30 years of archives from 3 pediatric hospitals and identified 18 solitary fibrous tumor diagnoses.…”

Prominent entrapment of respiratory epithelium in primary and metastatic intrapulmonary non-epithelial neoplasms: a frequent morphological pattern closely mimicking adenofibroma and other biphasic pulmonary lesions

“…Pulmonary adenofibroma (PAF) is the most frequent and the most striking and misleading pattern Table 2 Entrapment of alveolar/respiratory epithelium in different primary and metastatic pulmonary lesions [6]. Following discovery of STAT6-NAB2 gene fusions as driver events in most of SFTs, STAT6 IHC has emerged as highly sensitive and specific marker for SFT [7][8][9]. In the pre-STAT6 era however, many PAF-like SFTs were misclassified as PAF.…”

Pediatric sellar solitary fibrous tumor/ hemangiopericytoma: A rare case report and review of the literature

“…A recent study[ 24 ] from three pediatric hospitals reevaluating prior pathology from the past 30 years found that 18 tumors total were classified as SFTs. However, when immunohistochemistry was performed on the tissue, only three tumors from two patients were found to be STAT6 positive; the remainder tumors required reclassification.…”