We herein describe soft tissue tumor arising in the lower extremity of a pediatric patient. The tumor displayed a unique and wide range of histological features, sheet-like and cohesive growth pattern consisting of enlarged round to epithelioid atypical cells with a large alveolar and pseudopapillary histological architecture, focally mimicking alveolar soft part sarcoma and MiT family translocation renal cell carcinoma. Tumor cells were focally immunoreactive for cytokeratin, S-100, and EMA. RNA sequencing identified a novel in-frame NR1D1 (exon 5)-MAML1 (exon 2) gene rearrangement resulting in the formation of a putative chimeric protein containing the N-terminal C4-type zing finger domains of NR1D1 and the C-terminal MAML1 protein, which was confirmed by subsequent RT-PCR, Sanger sequencing, and FISH assay. To the best of our knowledge, NR1D1-MAML1 fusion has not yet been described in any neoplasms, suggesting the emergence of a novel tumor entity.

我们在此描述了在小儿患者下肢出现的软组织肿瘤。肿瘤表现出独特而广泛的组织学特征，片状和内聚性生长模式，由圆形到上皮样非典型细胞扩大，具有大的肺泡和假乳头状组织学结构，集中模仿肺泡软部分肉瘤和MiT家族易位性肾细胞癌。肿瘤细胞对细胞角蛋白，S-100和EMA具有局部免疫反应性。RNA测序鉴定了一种新型的读框内NR1D1（外显子5）-MAML1（第2外显子）基因重排导致形成了一个推定的嵌合蛋白，该蛋白包含NR1D1的N端C4型zeing指结构域和C端MAML1蛋白，这一点已通过随后的RT-PCR，Sanger测序和FISH证实分析。据我们所知，尚未在任何肿瘤中描述NR1D1-MAML1融合体，表明出现了新型肿瘤实体。