间充质软骨肉瘤 (MCS) 是一种罕见的软骨肉瘤亚型，发生在广泛的解剖部位，如骨、软组织和颅内部位。中枢神经系统 (CNS) 是骨外 MCS 最常见的起源之一。然而，在该肿瘤中尚未报道替代的 HEY1::NCOA2 融合。我们报告了一例伴有 HEY1::NCOA2 重排的颅内 MCS 病例。一名 52 岁女性在蝶鞍周围发现 15 毫米的钙化肿块。她最初接受了经蝶手术切除肿瘤，然后在 5 年内针对 5 次局部复发进行了额外切除。组织学上，肿瘤由小圆形至纺锤形细胞与分化良好的透明软骨岛混合组成。还观察到血管外皮细胞瘤样血管模式和小窦状血管。使用从上次操作的福尔马林固定石蜡包埋样品中提取的 RNA 进行 RNA 测序，揭示了 HEY1::NCOA2 融合的两种替代变体：HEY1(ex4)::NCOA2 (ex13) 和 HEY1(ex4)::NCOA2(ex14) 。使用逆转录聚合酶链式反应，这两种变体均被确认为框内融合。软骨成分在复发过程中通常不明显。除了非典型的病理发现外，手术标本的RNA质量差和非特异性STAT6核染色也阻碍了正确诊断。这是首例报告的颅内MCS具有替代HEY1::NCOA2融合的病例。版权所有 © 2024 Kishikawa、Kondo、Yao 和 Saito。

Mesenchymal chondrosarcoma (MCS) is a rare subtype of chondrosarcoma that occurs at widespread anatomical locations, such as bone, soft tissue, and intracranial sites. The central nervous system (CNS) is one of the most common origins of extraosseous MCS. However, alternative HEY1::NCOA2 fusions have not been reported in this tumor.We report a case of intracranial MCS with HEY1::NCOA2 rearrangement. A 52-year-old woman presented with a 15-mm calcified mass around the sella turcica. She initially underwent transsphenoidal surgery for tumor resection and then additional resections for five local recurrences over 5 years. Histologically, the tumor was composed of small round to spindle-shaped cells admixed with well-differentiated hyaline cartilaginous islands. A hemangiopericytoma-like vascular pattern and small sinusoid-like vessels were also observed. RNA sequencing using RNA extracted from formalin-fixed paraffin-embedded samples from the last operation revealed two alternative variants of the HEY1::NCOA2 fusion: HEY1(ex4)::NCOA2 (ex13) and HEY1(ex4)::NCOA2(ex14). Both variants were confirmed as in-frame fusions using reverse transcription-polymerase chain reaction.Cartilaginous components were often not apparent during the recurrences. In addition to the non-typical pathological finding, the correct diagnosis was hampered by the poor RNA quality of the surgical specimens and non-specific STAT6 nuclear staining.This is the first reported case of intracranial MCS with an alternative HEY1::NCOA2 fusion.Copyright © 2024 Kishikawa, Kondo, Yao and Saito.