Desmoplastic small round cell tumors (DSRCTs) are highly aggressive sarcomas that most commonly occur intra‐abdominally, and are defined by EWSR1‐WT1 gene fusion. Intracranial DSRCTs are exceptionally rare with only seven previously reported fusion‐positive cases. Herein, we evaluate the clinical, morphologic, immunohistochemical and molecular features of five additional examples. All patients were male (age range 6–25 years; median 11 years), with four tumors located supratentorially and one within the posterior fossa. The histologic features were highly variable including small cell, embryonal, clear cell, rhabdoid, anaplastic and glioma‐like appearances. A prominent desmoplastic stroma was seen in only two cases. The mitotic index ranged from <1 to 12/10 HPF (median 5). While all tumors showed strong desmin positivity, epithelial markers such as EMA, CAM 5.2 and other keratins were strongly positive in only one, focally positive in two and negative in two cases. EWSR1‐WT1 gene fusion was present in all cases, with accompanying mutations in the TERT promoter or STAG2 gene in individual cases. Given the significant histologic diversity, in the absence of genetic evaluation these cases could easily be misinterpreted as other entities. Desmin immunostaining is a useful initial screening method for consideration of a DSRCT diagnosis, prompting confirmatory molecular testing. Demonstrating the presence of an EWSR1‐WT1 fusion provides a definitive diagnosis of DSRCT. Genome‐wide methylation profiles of intracranial DSRCTs matched those of extracranial DSRCTs. Thus, despite the occasionally unusual histologic features and immunoprofile, intracranial DSRCTs likely represent a similar, if not the same, entity as their soft tissue counterpart based on the shared fusion and methylation profiles.

中文翻译：

---

颅内增生性小圆形细胞瘤的临床病理和分子特征

促结缔组织增生性小圆细胞肿瘤（DSRCTs）是最常发生腹内，并且通过定义高度攻击性肉瘤EWSR1 - WT1基因融合。颅内DSRCT极少见，以前仅报道过7例融合阳性病例。本文中，我们评估了另外五个实例的临床，形态，免疫组化和分子特征。所有患者均为男性（年龄范围6–25岁；中位11岁），其中4例位于幕上肿瘤，1例位于后颅窝内。组织学特征高度可变，包括小细胞，胚胎，透明细胞，横纹肌，间变性和神经胶质瘤样外观。仅在两个病例中观察到突出的增生基质。有丝分裂指数范围从<1到12/10 HPF（中位数5）。尽管所有肿瘤均表现出强的结蛋白阳性，但上皮标记物（例如EMA，CAM 5.2和其他角蛋白）仅在一种情况下为强阳性，在两种情况下为局部阳性，在两种情况下为阴性。在所有情况下均存在EWSR1 - WT1基因融合，个别情况下TERT启动子或STAG2基因伴随突变。鉴于明显的组织学多样性，在没有基因评估的情况下，这些病例很容易被误解为其他实体。结蛋白免疫染色是考虑DSRCT诊断的有用的初始筛选方法，可促进进行确证的分子检测。展示的存在EWSR1 - WT1融合提供了DSRCT的明确诊断。颅内DSRCT的全基因组甲基化谱与颅外DSRCT的基因组甲基化谱匹配。因此，尽管偶尔有异常的组织学特征和免疫特性，但基于共享的融合和甲基化特性，颅内DSRCT可能代表与其软组织对应物相似的实体，即使不是相同的实体。