FIGURE 1.

Radiological, pathological and molecular features of Case 1. (A) The axial FLAIR and T1‐weighted MRI sequences revealed a large, well‐defined, solid mass in the right frontal lobe, causing a slight displacement of the midline structures towards the left side. (B) H&E staining showed a prominent ependymoma‐like pattern characterized by abundant perivascular pseudorosettes. (C) The tumour was distinctly separated from the surrounding brain tissue. (D) Some areas shown a dense‐arranged and ribbon‐like pattern with remarkable nuclear atypia. (E) Extensively calcified foci were observed. The tumour cells were partially positive for Oligo‐2 (F) and diffusely immunopositive for CD56 (G). (H) Methylation‐based unsupervised hierarchical clustering analysis of Case 1 with selected reference cases, including BCOR‐ITD and other potential mimic entities (n = 138). (I) Methylation‐based t‐SNE analysis together with selected reference groups. (J) Methylation‐based copy number variations of Case 1. (K–M) Graphical depiction and validation of BCOR fusions in Case 1: BCOR (blue), EP300 (purple) and L3MBTL2 (yellow) with breakpoints (the red line). Agarose electrophoresis of RT–PCR and Sanger sequencing of the amplified products confirmed the fusions of EP300::BCOR and BCOR::L3MBTL2.