According to the fifth edition of the World Health Organization (WHO) classification of tumors of the central nervous system (CNS), diffuse midline glioma H3 K27-altered is a grade 4 infiltrative glioma that arises from midline anatomical structures and is characterized by the loss of H3 K27me3 and co-occurring H3 K27M mutation or EZHIP overexpression. However, the H3 K27M mutation has also been observed in circumscribed gliomas and glioneuronal tumors arising in midline anatomical structures, which may result in diagnostic pitfalls.

Rosette-forming glioneuronal tumor (RGNT) is a CNS WHO grade 1 neoplasm that histologically features neurocytic and glial components and originates in midline anatomical structures.

This study aimed to assess whether RGNTs, similar to other midline tumors, may exhibit immunohistochemical loss of H3 K27me3 and harbor the H3 K27M mutation.

All seven analyzed RGNTs displayed immunohistochemical loss of H3 K27me3 in all tumor cells or H3 K27me3 mosaic immunostaining. In one case, H3 K27me3 loss was associated with the H3 K27M mutation, whereas the other six cases did not exhibit any H3 mutations or EZHIP overexpression. During a follow-up period of 23 months, the H3 K27M-mutant case remained unchanged in size despite partial resection, indicating that the H3 mutation may not confer higher biological aggressiveness to RGNT.

The immunohistochemical loss of H3 K27me3 co-occurring with the H3 K27M mutation may result in the potential misdiagnosis of RGNT, especially in cases of small biopsy specimens consisting of only the glial component.

根据世界卫生组织 (WHO) 第五版中枢神经系统 (CNS) 肿瘤分类，弥漫性中线胶质瘤 H3 K27 改变是一种 4 级浸润性胶质瘤，起源于中线解剖结构，其特征是丢失H3 K27me3 和同时发生的H3 K27M 突变或 EZHIP 过表达。然而，在中线解剖结构中出现的局限性胶质瘤和胶质神经元肿瘤中也观察到了H3 K27M 突变，这可能会导致诊断陷阱。

玫瑰花结形成性胶质神经元肿瘤 (RGNT) 是一种中枢神经系统 WHO 1 级肿瘤，其组织学特征为神经细胞和神经胶质成分，起源于中线解剖结构。

本研究旨在评估 RGNT 是否与其他中线肿瘤类似，可能表现出 H3 K27me3 的免疫组织化学缺失并含有H3 K27M 突变。

所有七个分析的 RGNT 均显示所有肿瘤细胞中 H3 K27me3 的免疫组织化学缺失或 H3 K27me3 镶嵌免疫染色。在一个病例中，H3 K27me3 缺失与H3 K27M 突变相关，而其他 6 个病例没有表现出任何H3突变或 EZHIP 过度表达。在23个月的随访期间，尽管部分切除， H3 K27M突变病例的大小仍保持不变，表明H3突变可能不会赋予RGNT更高的生物攻击性。

H3 K27me3 的免疫组织化学缺失与H3 K27M 突变同时发生可能会导致 RGNT 的潜在误诊，特别是在仅由神经胶质成分组成的小活检标本的情况下。