INTRODUCTION

Choroid plexus tumours are intraventricular neoplasms derived from the choroid plexus epithelium. In contrast to choroid plexus papilloma, choroid plexus carcinoma shows frank signs of malignancy and is associated with infancy, TP53 alterations and an aggressive clinical course.¹ DNA methylation profiling segregates choroid plexus tumours into three distinct epigenetic subgroups: supratentorial paediatric low-risk choroid plexus tumours, infratentorial adult low-risk choroid plexus tumours and supratentorial paediatric high-risk choroid plexus tumours (subclass paediatric B).^2-4 Choroid plexus tumours may acquire unusual histological features (e.g. oncocytic change, mucinous degeneration, melanisation, tubular/glandular architecture, neuropil-like islands, bone, cartilage or adipose tissue formation) and may also show unstructured solid growth.⁵ A malignant choroid plexus tumour with prevailing blastematous features, however, has not yet to our knowledge been reported.

A 3-year-old girl, with a family history of neuroblastoma (first cousin), suffered from intracranial hypertension due to a large tumour located within the left lateral ventricle showing heterogeneous contrast enhancement (Figure 1A). Gross total resection was achieved. Upon histopathological examination, the highly cellular tumour displayed a pleomorphic spindle cell mesenchymal component rich in connective tissue and elastic material with transitions to immature poorly differentiated blastematous cells arranged in nests (Figure 1B–D). Focally, there was a papillary growth pattern reminiscent of the non-neoplastic choroid plexus (Figure 1E). Mitotic activity was elevated, and microvascular proliferation and tumour necrosis were present. Using immunohistochemical staining, the tumour cells displayed polyphenotypic differentiation with positivity for cytokeratins (MNF116) and vimentin, but also focal staining for GFAP, synaptophysin, MITF, HMB45, smooth muscle actin and desmin (Figure S1). Expressions of CK18 and membranous staining of the choroid plexus tumour marker Kir7.1 were encountered in areas of focal papillary growth but gradually lost in tumour cells showing a less differentiated phenotype (inset Figure 1E). Staining for SALL4, EMA, myogenin, Olig2, p53, Lin28A, NUT, BCOR and germinal markers (OCT3/4, PLAP, beta-HCG and alpha-fetoprotein) were negative. Silver impregnation stains showed the reticulin network in the tumour was abundant. Nuclear expression of SMARCB1/INI1 and SMARCA4/Brg1 was retained (normal). The Ki67/MIB-labelling index was 70% in the poorly differentiated component. Custom panel sequencing (including TP53, DICER1, DROSHA and DGCR8 genes) performed on germline and tumour DNA did not reveal any pathogenic alterations. Using RNAseq (TruSeq RNA Library Prep; Illumina) and a set of fusion detection tools (FusionMAP, FusionCatcher, STAR-fusion and Defuse), no fusion transcripts could be identified. Copy number profiling showed gains of chromosome 2, 7, 8,12, 19 and 20 and a more focal amplification of 300 Kb on chromosome 20q11.2 containing the genes XKR7, CCM2L, HCK, TM9SF4 and PLAGL2 (Figure S2).

DNA-methylation profiling (Illumina Methylation EPIC BeadChip) using the Heidelberg central nervous system (CNS) tumour classifier³ showed the case to be a ‘choroid plexus tumour, subclass paediatric B’ (calibrated score 0.99), and the similarity with this molecular subgroup was further confirmed by t-SNE analysis (Figure 1F). Based on the histopathological features of this malignant choroid plexus tumour, a diagnosis of choroid plexus tumour with immature blastematous elements was established. The patient received conventional and high-dose chemotherapy followed by proton therapy. Seventeen months after the initial resection, a distant recurrence affecting the right parietal lobe was detected on follow-up imaging and subsequently confirmed by biopsy.

Blastomas are malignant childhood neoplasms composed of immature elements, which are thought to recapitulate early stages of organ development. A solid growth pattern with mixed layers showing mesenchymal and blastematous differentiation is the hallmark feature of pleuropulmonary blastomas but has also been described in blastomas found in other locations. The histopathological similarity of the present case showing immature blastematous and mesenchymal elements could justify a diagnosis of choroid plexus blastoma.

As in the majority of choroid plexus tumours, genetic events that drive the development of choroid plexus tumour with immature blastematous elements remain to be determined.⁶ The absence of somatic and germline DICER1 mutations in the present case argues against a link with DICER1-associated entities such as pituitary blastoma, pineoblastoma, DICER1-associated CNS sarcoma and embryonal tumour with multilayered rosettes.^{7, 8}

DNA methylation profiles represent a combination of both somatically acquired DNA methylation changes and a signature reflecting the cell of origin. The high similarity of the DNA methylation profile with choroid plexus tumours of the molecular subclass paediatric B is characteristic for malignant choroid plexus tumours and may suggest that the tumour secondarily acquired blastematous features. Among choroid plexus tumours from our archives (including 102 cases of the molecular subclass paediatric B), no further cases with immature blastematous elements were encountered, suggesting that immature blastematous elements are not a characteristic feature of molecular subclass paediatric B tumours. Clinical history, immunohistochemical staining profile and molecular findings argue not only against the possibility of other CNS tumour entities but also against metastatic disease, which is frequent in pleuropulmonary blastoma patients.⁹ We had initially also considered the possibility of teratoma, but the histopathological features would be unusual, and the DNA methylation profiling results make this possibility unlikely.

To conclude, malignant choroid tumours may show prevailing immature blastematous elements, that show similarities with blastomas found in other locations. This case also highlights the value of DNA-methylation profiling in the diagnosis of choroid plexus tumours with unusual histopathological features.

中文翻译：

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一种恶性脉络丛肿瘤，主要有未成熟胚细胞成分

介绍

脉络丛肿瘤是源自脉络丛上皮的脑室内肿瘤。与脉络丛乳头状瘤相反，脉络丛癌显示出明显的恶性肿瘤迹象，并与婴儿期、TP53改变和侵袭性临床病程有关。¹ DNA 甲基化分析将脉络丛肿瘤分为三个不同的表观遗传亚组：幕上小儿低危脉络丛肿瘤、幕下成人低危脉络丛肿瘤和幕上小儿高危脉络丛肿瘤（小儿 B 亚类）。^2-4脉络丛肿瘤可能获得不寻常的组织学特征（例如嗜酸细胞变化、粘液变性、黑色素化、管状/腺体结构、神经纤维样岛、骨、软骨或脂肪组织形成），也可能表现出非结构化的实体生长。⁵然而，据我们所知，尚未报道具有主要胚泡特征的恶性脉络丛肿瘤。

一名 3 岁女孩，有神经母细胞瘤家族史（堂兄），由于位于左侧脑室内的大肿瘤显示不均匀的对比增强，患有颅内高压（图 1A）。实现了总切除。经组织病理学检查，高细胞肿瘤显示出多形性梭形细胞间充质成分，富含结缔组织和弹性材料，并转变为排列成巢状的未成熟低分化胚细胞（图 1B-D）。局部地，有一种乳头状生长模式，让人联想到非肿瘤性脉络丛（图 1E）。有丝分裂活性升高，存在微血管增生和肿瘤坏死。使用免疫组化染色，肿瘤细胞表现出多表型分化，对细胞角蛋白（MNF116）和波形蛋白呈阳性，但对 GFAP、突触素、MITF、HMB45、平滑肌肌动蛋白和结蛋白也有局灶染色（图 S1）。CK18 的表达和脉络丛肿瘤标志物 Kir7.1 的膜染色出现在局灶性乳头状生长区域，但在表现出分化程度较低的表型的肿瘤细胞中逐渐消失（插图 1E）。SALL4、EMA、肌细胞生成素、Olig2、p53、Lin28A、NUT、BCOR 和生发标志物（OCT3/4、PLAP、β-HCG 和甲胎蛋白）染色均为阴性。银浸渍染色显示肿瘤中的网状蛋白网络丰富。SMARCB1/INI1 和 SMARCA4/Brg1 的核表达被保留（正常）。Ki67/MIB 标记指数在低分化成分中为 70%。对种系和肿瘤 DNA 进行的TP53、DICER1、DROSHA和DGCR8基因）未发现任何致病性改变。使用 RNAseq（TruSeq RNA Library Prep；Illumina）和一组融合检测工具（FusionMAP、FusionCatcher、STAR-fusion 和 Defuse），无法识别出融合转录本。拷贝数分析显示染色体 2、7、8、12、19 和 20 的增加和染色体 20q11.2 上 300 Kb 的更集中扩增，包含基因XKR7、CCM2L、HCK、TM9SF4和PLAGL2（图 S2）。

使用 Heidelberg 中枢神经系统 (CNS) 肿瘤分类器³进行的 DNA 甲基化分析 (Illumina Methylation EPIC BeadChip)显示该病例为“脉络丛肿瘤，儿科 B 亚类”（校准分数 0.99），并且与该分子亚群相似t-SNE 分析进一步证实了这一点（图 1F）。基于这种恶性脉络丛肿瘤的组织病理学特征，确立了具有未成熟胚细胞成分的脉络丛肿瘤的诊断。患者接受常规和大剂量化疗，随后接受质子治疗。初次切除 17 个月后，在随访影像中检测到影响右顶叶的远处复发，随后通过活检证实。

母细胞瘤是由未成熟元素组成的恶性儿童肿瘤，被认为概括了器官发育的早期阶段。具有显示间充质和胚细胞分化的混合层的固体生长模式是胸膜肺母细胞瘤的标志性特征，但也已在其他部位发现的母细胞瘤中有所描述。本例显示未成熟胚细胞和间充质成分的组织病理学相似性可以证明脉络丛母细胞瘤的诊断是合理的。

与大多数脉络丛肿瘤一样，驱动具有未成熟胚细胞成分的脉络丛肿瘤发展的遗传事件仍有待确定。⁶在本病例中，体细胞和种系DICER1突变的缺失与DICER1相关实体（如垂体母细胞瘤、松果体母细胞瘤、DICER1相关 CNS 肉瘤和具有多层玫瑰花结的胚胎肿瘤）之间存在联系。^7、8

DNA 甲基化谱代表了体细胞获得的 DNA 甲基化变化和反映细胞来源的特征的组合。DNA 甲基化谱与儿科 B 分子亚类脉络丛肿瘤的高度相似性是恶性脉络丛肿瘤的特征，并且可能表明肿瘤继发获得胚泡特征。在我们档案中的脉络丛肿瘤（包括 102 例小儿 B 分子亚类）中，未发现更多具有未成熟胚细胞成分的病例，这表明未成熟胚细胞成分不是儿科 B 分子肿瘤的特征。临床病史，⁹我们最初也考虑过畸胎瘤的可能性，但组织病理学特征不寻常，DNA 甲基化分析结果使这种可能性不太可能。

总而言之，恶性脉络膜肿瘤可能表现出普遍的未成熟胚细胞成分，这与在其他位置发现的胚细胞有相似之处。该病例还突出了 DNA 甲基化分析在诊断具有异常组织病理学特征的脉络丛肿瘤中的价值。