Recurrent BRAF Gene Fusions in a Subset of Pediatric Spindle Cell Sarcomas: Expanding the Genetic Spectrum of Tumors With Overlapping Features With Infantile Fibrosarcoma. (January 2018)

• Record Type: Journal Article
• Authors: Kao, Yu-Chien; Fletcher, Christopher D.M.; Alaggio, Rita; Wexler, Leonard; Zhang, Lei; Sung, Yun-Shao; Orhan, Dicle; Chang, Wei-Chin; Swanson, David; Dickson, Brendan C.; Antonescu, Cristina R.
• Is Part Of: American journal of surgical pathology. Volume 42:Number 1(2018)
• Publication Date: 2018-01
• Subjects: fibrosarcoma -- infantile fibrosarcoma -- BRAF -- NTRK1 -- NTRK3 -- fusions; Pathology, Surgical -- Periodicals; 617.0705
• DOI: 10.1097/PAS.0000000000000938
• Languages: English
• ISSNs: 0147-5185

Abstract

Abstract : Infantile fibrosarcomas (IFS) represent a distinct group of soft tissue tumors occurring in patients under 2 years of age and most commonly involving the extremities. Most IFS show recurrent ETV6-NTRK3 gene fusions, sensitivity to chemotherapy, and an overall favorable clinical outcome. However, outside these well-defined pathologic features, no studies have investigated IFS lacking ETV6-NTRK3 fusions, or tumors with the morphology resembling IFS in older children. This study was triggered by the identification of a novel SEPT7-BRAF fusion in an unclassified retroperitoneal spindle cell sarcoma in a 16-year-old female by targeted RNA sequencing. Fluorescence in situ hybridization screening of 9 additional tumors with similar phenotype and lacking ETV6-NTRK3 identified 4 additional cases with BRAF gene rearrangements in the pelvic cavity (n=2), paraspinal region (n=1), and thigh (n=1) of young children (0 to 3 y old). Histologically, 4 cases including the index case shared a fascicular growth of packed monomorphic spindle cells, with uniform nuclei and fine chromatin, and a dilated branching vasculature; while the remaining case was composed of compact cellular sheets of short spindle to ovoid cells. In addition, a minor small blue round cell component was present in 1 case. Mitotic activity ranged from 1 to 9/10 high power fields. Immunohistochemical stains were nonspecific, with only focal smooth muscle actin staining demonstrated in 3 cases tested. Of the remaining 5 BRAF negative cases, further RNA sequencing identified 1 case with EML4-NTRK3 in an 1-year-old boy with a foot IFS, and a second case with TPM3-NTRK1 fusion in a 7-week-old infant with a retroperitoneal lesion. Our findings of recurrent BRAF gene rearrangements in tumors showing morphologic overlap with IFS expand the genetic spectrum of fusion-positive spindle cell sarcomas, to include unusual presentations, such as older children and adolescents and predilection for axial location, thereby opening new opportunities for kinase-targeted therapeutic intervention. Abstract : Supplemental Digital Content is available in the text.