PRRX1 -rearranged Fibroblastic Tumors : A Clinicopathologic and Molecular Study of 18 Cases Including a Novel PRRX1::EP300 Fusion

Dehner CA, Torres-Mora J, Thangaiah JJ, Oliveira A, Michal M, Malik F, Din NU, Hassan U, Maqbool H, Obeidin F, Caragea M, Lee CH, Schubart C, Agaimy A, Grundtmann B, Melchior L, Talman ML, Gross J, Cheah AL, Thway K, Fisher C, Antonescu CR, Linos K (2026)

Publication Type: Journal article

Publication year: 2026

Journal

American Journal of Surgical Pathology Lippincott, Williams & Wilkins

Book Volume: 50

Pages Range: 31-40

Journal Issue: 1

DOI: 10.1097/PAS.0000000000002472

Abstract

With the first series of PRRX1 -rearranged tumors published in 2019, the spectrum of these so-called fibroblastic tumors has been expanded. Since then, several smaller case series have been published; however, our understanding of them continues to be quite limited given their rarity. We herein studied 18 additional cases, the largest series to date. Eighteen tumors present in 9 male, 8 female, and 1 nonbinary patient with a median age of 35 years (range: 11 to 70 y) and involved the neck (5), the chest region (4), thigh (3), back (1), shoulder (1), forehead (1), lower leg (1), axilla (1), and the parapharyngeal region (1). Clinical follow-up (9/18 tumors; 50%; median: 10 mo; range: 4 to 40 mo) showed consistent indolent behavior without local recurrences or distant metastases. On morphology, these tumors were characterized by well-circumscription and distinctive peripheral crescent-shaped vessels. They were composed of uniform spindle and round cells growing in short fascicles within often densely hyalinized collagen lacking significant mitotic activity, necrosis, or cytologic atypia. Immunohistochemically, about half of the tested tumors expressed focal to rarely diffuse S100 with occasional co-expression of SOX10. Interestingly, almost half of the tested cases also showed complete loss of RB expression. All but 1 tumor harbored a PRRX1::NCOA1 fusion, while 1 case harbored a novel PRRX1::EP300 fusion. We herein provide additional data on these exceptionally uncommon tumors, expand their molecular spectrum, and compare them to their close morphologic mimics to aid in accurate diagnosis and avoid confusion with potentially more aggressive neoplasms.

Authors with CRIS profile

Christoph Schubart Institute of Pathology Abbas Agaimy Institute of Pathology

Involved external institutions

Indiana University – Purdue University Indianapolis US United States (USA) (US) Mayo Clinic US United States (USA) (US) Univerzita Karlova v Praze / Charles University in Prague CZ Czech Republic (CZ) St. Jude Children’s Research Hospital US United States (USA) (US) University of Miami US United States (USA) (US) Shaukat Khanum Memorial Cancer Hospital & Research Centre (SKMCH) PK Pakistan (PK) Northwestern University US United States (USA) (US) University of Alberta CA Canada (CA) The Institute of Cancer Research (ICR) GB United Kingdom (GB) Memorial Sloan Kettering Cancer Center US United States (USA) (US) Sjællands Universitetshospital, Roskilde DK Denmark (DK) Rigshospitalet DK Denmark (DK) Johns Hopkins Hospital US United States (USA) (US) Sonic Healthcare Limited AU Australia (AU)

How to cite

APA:

Dehner, C.A., Torres-Mora, J., Thangaiah, J.J., Oliveira, A., Michal, M., Malik, F.,... Linos, K. (2026). PRRX1 -rearranged Fibroblastic Tumors : A Clinicopathologic and Molecular Study of 18 Cases Including a Novel PRRX1::EP300 Fusion. American Journal of Surgical Pathology, 50(1), 31-40. https://doi.org/10.1097/PAS.0000000000002472

MLA:

Dehner, Carina A., et al. "PRRX1 -rearranged Fibroblastic Tumors : A Clinicopathologic and Molecular Study of 18 Cases Including a Novel PRRX1::EP300 Fusion." American Journal of Surgical Pathology 50.1 (2026): 31-40.

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