FGFR1 gene fusions in a subset of pediatric mesenchymal tumors: Expanding the genetic spectrum of tumors sharing histologic overlap with infantile fibrosarcoma and “NTRK‐rearranged” spindle cell neoplasms

• DOI: 10.1002/gcc.23179
• Publication Date: 2023-06-02T14:40:11Z
• Authors: Laura M. Warmke; Alyaa Al‐Ibraheemi; Larry Wang; David Parham; Erin R. Rudzinski; Bradley A. Stohr; Carina Miles; Omar Habeeb; Jessica L. Davis
• Keywords: Male; Fibrosarcoma; Biomarkers, Tumor; Humans; Infant; Female; Soft Tissue Neoplasms; Receptor, Fibroblast Growth Factor, Type 1; Gene Fusion; Receptor, trkA; Neoplasms, Connective and Soft Tissue

Abstract As the classification of kinase‐driven spindle cell tumors continues to evolve, we describe first series pediatric mesenchymal harboring FGFR1 gene fusions that share histologic overlap with infantile fibrosarcoma and “ NTRK ‐rearranged” neoplasms. Herein, present three cases ‐rearranged tumors, including one case :: PARD6B fusion two EBF2 fusion. The involved infants ranging from 3 9 months in age a male‐to‐female ratio 2:1. All deep soft tissue gluteal, pelvic, or perirectal region. Histologically, comprised cellular neoplasm primitive stellate cells, focal myxoid stroma, epithelioid features, no necrosis, occasional mitotic figures (2–6 per 10 high‐power field). By immunohistochemistry, neoplastic cells focally expressed CD34 but lacked expression S100 protein, SMA, desmin, myogenin, MyoD1, pan‐TRK, ALK. These cases, long‐term clinical follow‐up, demonstrate occur subset newly described locally aggressive behavior. Importantly, knowledge these genetic alterations this spectrum is key for diagnostic targeted therapeutic purposes.