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<p>Mesenchymal tumors of the gastrointestinal (GI) tract include a range of entities such as gastrointestinal stromal tumor (GIST), schwannoma, and leiomyoma; however, the genetic background of GI leiomyomas has not been elucidated. Herein, we report a case of rectal myxoid epithelioid smooth muscle tumor harboring a novel <i>MEF2A</i>::<i>NCOA2</i> gene fusion. A 67-year-old male presented with a 16&#xa0;mm tumor in the lower rectum. Pathological examination revealed a well-circumscribed lesion within the muscularis mucosae, characterized by epithelioid to spindle cells arranged in a myxoid matrix. The tumor cells displayed minimal cytological atypia and no mitotic figures. Immunohistochemistry showed strong positivity for desmin, α-SMA, h-caldesmon, and CD34, and weak DOG1 positivity. RNA sequencing revealed an in-frame <i>MEF2A</i>::<i>NCOA2</i> fusion, which was confirmed by direct sequencing. Fluorescence in situ hybridization further verified <i>NCOA2</i> rearrangement. This novel fusion gene may have been functional in this case, serving as a driver. Recently, 5 myxoid epithelioid smooth muscle tumors with <i>MEF2D</i>::<i>NCOA2</i> gene fusion were reported in the vulvovaginal region. Given the characteristic histological and molecular findings, this case may represent a new entity in the gastrointestinal tract related to the vulvovaginal tumor, serving as a foundation for future studies.</p>

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Myxoid epithelioid smooth muscle tumor with a novel MEF2A::NCOA2 fusion arising in the rectum: case report and literature review

  • 期刊论文

  • 发表日期：

    2025年9月24日

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  • Junko Kunieda,
  • Kyoko Yamashita,
  • Akito Dobashi,
  • Yuki Togashi,
  • Satoko Baba,
  • Norihito Inoue,
  • Kaoru Nakano,
  • Akiko Chino,
  • Shoichi Saito,
  • Noriko Yamamoto,
  • Hiroshi Kawachi,
  • Kengo Takeuchi

摘要

Mesenchymal tumors of the gastrointestinal (GI) tract include a range of entities such as gastrointestinal stromal tumor (GIST), schwannoma, and leiomyoma; however, the genetic background of GI leiomyomas has not been elucidated. Herein, we report a case of rectal myxoid epithelioid smooth muscle tumor harboring a novel MEF2A::NCOA2 gene fusion. A 67-year-old male presented with a 16 mm tumor in the lower rectum. Pathological examination revealed a well-circumscribed lesion within the muscularis mucosae, characterized by epithelioid to spindle cells arranged in a myxoid matrix. The tumor cells displayed minimal cytological atypia and no mitotic figures. Immunohistochemistry showed strong positivity for desmin, α-SMA, h-caldesmon, and CD34, and weak DOG1 positivity. RNA sequencing revealed an in-frame MEF2A::NCOA2 fusion, which was confirmed by direct sequencing. Fluorescence in situ hybridization further verified NCOA2 rearrangement. This novel fusion gene may have been functional in this case, serving as a driver. Recently, 5 myxoid epithelioid smooth muscle tumors with MEF2D::NCOA2 gene fusion were reported in the vulvovaginal region. Given the characteristic histological and molecular findings, this case may represent a new entity in the gastrointestinal tract related to the vulvovaginal tumor, serving as a foundation for future studies.