STAT6 Reliably Distinguishes Solitary Fibrous Tumors from Myofibromas

Abstract

Solitary fibrous tumors (SFT) and myofibromas (MF) historically have belonged to the same morphologic spectrum and have been lumped together under the nonspecific umbrella term, "hemangiopericytoma" along with other pericytic/myoid tumors. While current evidence shows clear distinction between the two entities, they frequently remain in the same histopathologic differential diagnosis. This diagnostic dilemma especially is common for smaller incisional biopsies from the oral cavity. STAT6 immunohistochemistry (IHC) recently was established as a reliable method to detect solitary fibrous tumor; however, the literature is sparse regarding STAT6 reactivity in MFs. The authors report ten new cases of oral solitary fibrous tumor, discuss histopathologic similarities and differences between the two tumors, and list respective STAT6 IHC expressivity. After IRB approval, 10 cases diagnosed as SFT and 24 cases of MF were collected from the University of Florida Oral and Maxillofacial Pathology Biopsy Service between the years 1994 and 2016. The original hematoxylin and eosin slides and related IHC were reviewed. IHC with STAT6 antibody was performed on all 34 samples, and the findings were analyzed. All cases were from the oral cavity or perioral regions. 10/10 SFTs expressed STAT6 nuclear reactivity, while no cases of MF showed nuclear expression of STAT6. STAT6 is a dependable marker to differentiate SFTs from MFs.

A Solitary Fibrous Tumor of the Eyelid

“…All ten SFTs were CD34 positive, while all other previously performed immunohistochemical stains were unreactive. STAT6 antibody nuclear reactivity was diffusely strong for 9/10 cases, while one case exhibited weak and focal nuclear reactivity 10. In our case, the tumor was positive for both CD34 and STAT6.…”

A case of solitary fibrous tumor/hemangiopericytoma in the central nervous system with papillary morphology

“…Literature from the past 5 years was searched, and we found that STAT6 immunohistochemistry has high specificity for SFT and that the diagnostic value of strong and diffuse nuclear expression of STAT6 in SFT has been proven . It was also found that STAT6 is a dependable marker to differentiate SFT from myofibromas . At the same time, follicular lymphoma‐associated STAT6 mutations facilitate nuclear residency of STAT6, while nuclear localization of STAT6 is also dramatically increased in Kaposi's sarcoma tissue .…”

“…[18][19][20] It was also found that STAT6 is a dependable marker to differentiate SFT from myofibromas. 21 At the same time, follicular lymphomaassociated STAT6 mutations facilitate nuclear residency of STAT6, 22 while nuclear localization of STAT6 is also dramatically increased in Kaposi's sarcoma tissue. 23 Doyle et al have reported that although the specificity of STAT6 immunodetection for the diagnosis of SFT in the appropriate morphological context is very high, dedifferentiated liposarcoma can resemble SFT morphologically and STAT6 expression in a subset of dedifferentiated liposarcoma could complicate this differential diagnosis.…”

Solitary Fibrous Tumor of the Cheek: Navigating Pathology and Advanced Multivariate Risk Stratification Assessment Models: A Clinicopathologic Challenge

“…The differential diagnosis for SFT encompasses several distinct entities, such as synovial sarcoma, deep fibrous histiocytoma, mammary-type myofibroblastoma, dermatofibrosarcoma protuberans, and pseudoangiomatous pattern of spindle cell lipoma. 16–18…”