CD34-negative Solitary Fibrous Tumor: A Clinicopathologic Study of 25 Cases and Comparison With Their CD34-positive Counterparts. (December 2021)

• Record Type: Journal Article
• Authors: Dermawan, Josephine K.; Rubin, Brian P.; Kilpatrick, Scott E.; Gjorgova Gjeorgjievski, Sandra; Fritchie, Karen J.; Goldblum, John R.; McKenney, Jesse K.; Billings, Steven D.
• Is Part Of: American journal of surgical pathology. Volume 45:Number 12(2021)
• Publication Date: 2021-12
• Subjects: solitary fibrous tumor -- CD34 -- STAT6 -- immunohistochemistry; Pathology, Surgical -- Periodicals; 617.0705
• DOI: 10.1097/PAS.0000000000001717
• Languages: English
• ISSNs: 0147-5185

Abstract

Abstract : CD34-negative solitary fibrous tumors (SFTs) are rare and have not been comprehensively studied. We retrospectively reviewed all cases of SFT confirmed with STAT6 immunohistochemistry and/or STAT6 gene fusion between 2013 and 2020 and collected pertinent clinicopathologic parameters. Of a total of 244 cases, 25 (10%) lacked CD34 expression by immunohistochemistry. Compared with CD34-positive SFT, CD34-negative SFT are more likely to arise in the head and neck area (32% vs. 24%, P =0.02) and present as metastatic disease (28% vs. 1%, P <0.0001). A significantly higher percentage of CD34-negative SFT exhibit high-grade cytologic atypia (hypercellularity, round cell or anaplastic morphology, nuclear pleomorphism, etc.) (48% vs. 22%, P =0.0073). There are no significant differences in the distributions of age, sex, tumor size, mitotic count, tumor necrosis, or risk stratification between CD34-negative and CD34-positive SFT. In addition, only 56% of CD34-negative SFT display a typical hemangiopericytoma-like vascular pattern. Special histologic features among CD34-negative SFT include prominent alternating hypercellular or fibrous and hypocellular myxoid areas with curvilinear vessels mimicking low-grade fibromyxoid sarcoma, pulmonary edema-like microcystic changes, and prominent amianthoid collagen fibers. In conclusion, compared with their CD34-positive counterparts, CD34-negative SFT is more likely to present as metastatic disease, show high-grade nuclear atypia, and lack the characteristic hemangiopericytoma-like vasculature, posing a unique diagnostic challenge. The use of STAT6 immunohistochemistry and/or molecular studies may be prudent in soft tissue tumors that appear CD34 negative and lack conventional SFT histopathologic characteristics.