Makise Naohiro, Mori Taisuke, Kobayashi Hiroshi, Nakagawa Kazuo, Ryo Eijitsu, Nakajima Jun, Kohsaka Shinji, Mano Hiroyuki, Aburatani Hiroyuki, Yoshida Akihiko, Ushiku Tetsuo
Department of Pathology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Department of Diagnostic Pathology, National Cancer Center Hospital, Tokyo, Japan.
Histopathology. 2020 Jun;76(7):1023-1031. doi: 10.1111/his.14080. Epub 2020 May 22.
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.
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.
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.
外胚间叶性软骨黏液样瘤（ECT）是一种罕见的口腔内良性肿瘤，几乎仅表现为舌背前部的小肿块。最近，在90%的ECT中发现了RREB1 - MRTFB（以前称为MKL2）融合基因，所有这些肿瘤均位于舌部，强调了其基因独特性。在此，我们报告两例发生于成年女性上纵隔的间叶性肿瘤，其具有RREB1 - MRTFB融合。
两例肿瘤均表现为边界清楚的椎旁肿块，临床怀疑为神经鞘瘤。在进行碎块切除后，27个月和18个月时均未观察到复发。尽管肿瘤最初无法分类，但二代测序检测到相同的RREB1（第8外显子）- MRTFB（第11外显子）融合转录本，通过逆转录聚合酶链反应、桑格测序和荧光原位杂交进行了验证。两例肿瘤均有玻璃样变区域，其中圆形细胞呈条索状或网状排列。肿瘤细胞显示出可能为退行性类型的轻度核异型性，有丝分裂活性极低，并且至少局灶性表达S100、胶质纤维酸性蛋白、平滑肌肌动蛋白和上皮膜抗原。总体而言，这些发现提示它们可能代表以前未描述过的累及纵隔的舌外ECT。然而，其组织学表现并非ECT的典型表现，因为病例2以梭形细胞的束状生长为主，而病例1的肿瘤缺乏黏液样改变。
我们首次提供证据表明RREB1 - MRTFB融合并不局限于头部区域的肿瘤，并且此类肿瘤是否代表舌外ECT需要进一步研究。
