Naohiro Makise1,2, Taisuke Mori2,3, Hiroshi Kobayashi4, Kazuo Nakagawa5, Eijitsu Ryo3, Jun Nakajima6, Shinji Kohsaka7, Hiroyuki Mano7, Hiroyuki Aburatani8, Akihiko Yoshida2,9, Tetsuo Ushiku1. 1. Department of Pathology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan. 2. Department of Diagnostic Pathology, National Cancer Center Hospital, Tokyo, Japan. 3. Division of Molecular Pathology, National Cancer Center Research Institute, Tokyo, Japan. 4. Department of Orthopaedic Surgery, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan. 5. Department of Thoracic Surgery, National Cancer Center Hospital, Tokyo, Japan. 6. Department of Thoracic Surgery, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan. 7. Division of Cellular Signaling, National Cancer Center Research Institute, Tokyo, Japan. 8. Genome Science Division, Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan. 9. Rare Cancer Center, National Cancer Center Hospital, Tokyo, Japan.
Abstract
AIMS: Ectomesenchymal chondromyxoid tumour (ECT) is a rare benign intraoral tumour which almost exclusively presents as a small mass of the anterior dorsal tongue. Recently, the RREB1-MRTFB (previously known as MKL2) fusion gene has been identified in 90% of ECTs, all located in the tongue, emphasising its genetic distinctiveness. Here, we report two mesenchymal tumours involving the superior mediastinum of adult women with RREB1-MRTFB fusions. METHODS AND RESULTS: Both tumours presented as well-circumscribed paravertebral masses that were clinically suspected to be schwannoma. After fragmented resection, recurrence was not observed at 27 and 18 months. Although tumours were originally unclassifiable, next-generation sequencing detected identical RREB1 (exon 8)-MRTFB (exon 11) fusion transcripts, which were validated by reverse transcriptase-polymerase chain reaction, Sanger sequencing, and fluorescence in-situ hybridisation. Both tumours shared hyalinised areas with round cells embedded in a cord or reticular manner. The tumour cells showed mild nuclear atypia of possible degenerative type with very low mitotic activity, and were at least focally positive for S100, glial fibrillary acidic protein, smooth muscle actin and epithelial membrane antigen. Overall, these findings suggest that they may represent previously undescribed extra-glossal ECT involving the mediastinum. However, the histology was not classic for ECT, because that in case 2 was predominated by storiform growth of spindle cells, whereas the tumour in case 1 lacked myxoid change. CONCLUSIONS: We have provided the first evidence that RREB1-MRTFB fusion is not limited to tumours in the head region, and whether such tumours represent extra-glossal ECTs requires further research.
AIMS: Ectomesenchymal chondromyxoid tumour (ECT) is a rare benign intraoral tumour which almost exclusively presents as a small mass of the anterior dorsal tongue. Recently, the RREB1-MRTFB (previously known as MKL2) fusion gene has been identified in 90% of ECTs, all located in the tongue, emphasising its genetic distinctiveness. Here, we report two mesenchymal tumours involving the superior mediastinum of adult women with RREB1-MRTFB fusions. METHODS AND RESULTS: Both tumours presented as well-circumscribed paravertebral masses that were clinically suspected to be schwannoma. After fragmented resection, recurrence was not observed at 27 and 18 months. Although tumours were originally unclassifiable, next-generation sequencing detected identical RREB1 (exon 8)-MRTFB (exon 11) fusion transcripts, which were validated by reverse transcriptase-polymerase chain reaction, Sanger sequencing, and fluorescence in-situ hybridisation. Both tumours shared hyalinised areas with round cells embedded in a cord or reticular manner. The tumour cells showed mild nuclear atypia of possible degenerative type with very low mitotic activity, and were at least focally positive for S100, glial fibrillary acidic protein, smooth muscle actin and epithelial membrane antigen. Overall, these findings suggest that they may represent previously undescribed extra-glossal ECT involving the mediastinum. However, the histology was not classic for ECT, because that in case 2 was predominated by storiform growth of spindle cells, whereas the tumour in case 1 lacked myxoid change. CONCLUSIONS: We have provided the first evidence that RREB1-MRTFB fusion is not limited to tumours in the head region, and whether such tumours represent extra-glossal ECTs requires further research.
Authors: Gunhild Mechtersheimer; Mindaugas Andrulis; Klaus-Wolfgang Delank; Anna-Lena Volckmar; Lei Zhang; Moritz von Winterfeld; Albrecht Stenzinger; Cristina R Antonescu Journal: Genes Chromosomes Cancer Date: 2021-04-10 Impact factor: 4.263