PRRX1-rearranged Fibroblastic Tumors

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.

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Publication Details

Journal
The American Journal of Surgical Pathology
Published
2025-10-02
DOI
https://doi.org/10.1097/pas.0000000000002472
Primary Topic
Soft tissue tumor case studies
Type
article
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article

PRRX1-rearranged Fibroblastic Tumors

Usman Hassan, Abbas Agaimy, Cheng‐Han Lee, Alison L. Cheah et al.
The American Journal of Surgical Pathology
Soft tissue tumor case studies
article

PRRX1-rearranged Fibroblastic Tumors

Usman Hassan, Abbas Agaimy, Cheng‐Han Lee, Alison L. Cheah, John Gross, Michael Michal, Linea Cecilie Melchior, Khin Thway, Judith Jebastin Thangaiah, Faizan Malik, Hina Maqbool, Farres Obeidin, Christoph D. Schubart, Mara Caragea, Carina Dehner, André M. Oliveira, Konstantinos Linos, Cyril Fisher, Cristina R. Antonescu, Nasir Ud Din, Jorge Torres‐Mora, Maj‐Lis Talman, Bo Grundtmann
article en

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.

The American Journal of Surgical PathologyVol. 50(1)
Northwestern University (US), Aga Khan University (PK), St. Jude Children's Research Hospital (US), Royal Marsden NHS Foundation Trust (GB), Mayo Clinic (US), Memorial Sloan Kettering Cancer Center (US), Institute of Cancer Research (GB), University of Miami (US), University of Alberta (CA), Friedrich-Alexander-Universität Erlangen-Nürnberg (DE), Charles University (CZ), Copenhagen University Hospital (DK), Rigshospitalet (DK), Zealand University Hospital (DK), Universitätsklinikum Erlangen (DE), Douglass Hanly Moir Pathology (AU), Mayo Clinic in Arizona (US), Biopticka Laborator (Czechia) (CZ), Shaukat Khanum Memorial Cancer Hospital and Research Center (PK), NIHR Surgical Reconstruction and Microbiology Research Centre (GB), Mayo Clinic in Florida (US), Johns Hopkins Hospital (US), Indiana University School of Medicine, Indiana University – Purdue University Indianapolis (US), University of Pennsylvania (US)
Openalex Percentile: Top 60%
Soft tissue tumor case studies
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