Open Access

BACKGROUND Diffuse pediatric-type high-grade gliomas (pedHGG), H3-wildtype and IDH-wildtype, encompass three main methylome-based subclasses: pedHGG-MYCN, -RTK1A/B/C, and -RTK2A/B. Since their first description in 2017, tumors of pedHGG-RTK2A/B have not been further characterized and their clinical significance is unknown. METHODS A not yet published cases series on pedHGG with a gliomatosis cerebri (GC) growth pattern showed an increased incidence of pedHGG-RTK2A/B (n=18/40). We assembled a cohort of 14 additional methylation-based pedHGG-RTK2A/B tumors and pooled them with the GC tumors providing centrally reviewed radiological, histological, and molecular characterization. RESULTS Our cohort of 32 pedHGG-RTK2A/B tumors consisted of 25 RTK2A (78%) and seven RTK2B (22%) cases. The median age was 11.6 years (4-17) with an overall survival of 15.9 months (interquartile range 12.1-25.8). Of the additional unselected cases with available imaging (10 of 14), seven showed a GC phenotype at diagnosis or follow-up. In addition, pedHGG-RTK2B tumors exhibited bithalamic involvement (6/7, 86%). Histopathology confirmed a diffuse glial neoplasm in all cases with prominent angiocentric features in both subclasses. Most tumors (24/29, 83%) diffusely expressed EGFR, notably with a focal perivascular enhancement. Cells of pedHGG-RTK2A lacked Olig2 expression, whereas 43% (3/7) of pedHGG-RTK2B expressed Olig2. Loss of ATRX expression occurred in four pedHGG-RTK2B samples (57%). In sequencing analyses (RTK2A: n=18, RTK2B: n=5), EGFR alterations (n=15/23, 65%; predominantly point mutations) were commonly found in both subclasses. Mutations in BCOR (n=14/18, 78%), SETD2 (n=7/18, 39%), and TERT promoter (n=6/18, 33%) occurred exclusively in pedHGG-RTK2A tumors, while pedHGG-RTK2B tumors were enriched for TP53 mutations (4/5, 80%). CONCLUSIONS In conclusion, genotype-phenotype correlations in a multicenter series of pedHGG-RTK2A/B tumors revealed a highly diffuse-infiltrating tumor frequently exhibiting a GC phenotype. The two subclasses share particular histomolecular features (EGFR alterations, angiocentric pattern), whereas they differ in specific characteristics (pedHGG-RTK2A: Olig2 negativity, BCOR and SETD2 mutations; pedHGG-RTK2B: ATRX and TP53 alterations).

Purpose Brain stem tumors in children < 3 months at diagnosis are extremely rare. Our aim is to study a retrospective cohort to improve the understanding of the disease course and guide patient management. Methods This is a multicenter retrospective analysis across the European Society for Pediatric Oncology SIOP-E HGG/DIPG Working Group linked centers, including patients with a brainstem tumor diagnosed between 2009 and 2020 and aged < 3 months at diagnosis. Clinical data were collected, and imaging characteristics were analyzed blindly and independently by two neuroradiologists. Results Five cases were identified. No patient received any therapy. The epicenter of two tumors was in the medulla oblongata alone and in the medulla oblongata and the pons in three. For patients with tumor in equal parts in the medulla oblongata and the pons (n = 3), the extension at diagnosis involved the spinal cord; for the two patients with the tumor epicenter in the medulla oblongata alone (n = 2), the extension at diagnosis included the pons (n = 2) and the spinal cord (n = 1). Biopsy was performed in one patient identifying a pilocytic astrocytoma. Two patients died. In one patient, autopsy revealed a high-grade glioma (case 3). Three survivors showed either spontaneous tumor regression (n = 2) or stable disease (n = 1). Survivors were followed up for 10, 7, and 0.6 years, respectively. One case had the typical imaging characteristics of a dorsal exophytic low-grade glioma. Conclusions No patient fulfilled the radiologic criteria defining a high-grade glioma. Central neuroradiological review and biopsy may provide useful information regarding the patient management.

Background The term gliomatosis cerebri (GC), a radiology-defined highly infiltrating diffuse glioma, has been abandoned since molecular GC-associated features could not be established. Methods We conducted a multinational retrospective study of 104 children and adolescents with GC providing comprehensive clinical and (epi-)genetic characterization. Results Median overall survival (OS) was 15.5 months (interquartile range, 10.9–27.7) with a 2-year survival rate of 28%. Histopathological grading correlated significantly with median OS: CNS WHO grade II: 47.8 months (25.2–55.7); grade III: 15.9 months (11.4–26.3); grade IV: 10.4 months (8.8–14.4). By DNA methylation profiling (n = 49), most tumors were classified as pediatric-type diffuse high-grade glioma (pedHGG), H3-/IDH-wild-type (n = 31/49, 63.3%) with enriched subclasses pedHGG_RTK2 (n = 19), pedHGG_A/B (n = 6), and pedHGG_MYCN (n = 5), but only one pedHGG_RTK1 case. Within the pedHGG, H3-/IDH-wild-type subgroup, recurrent alterations in EGFR (n = 10) and BCOR (n = 9) were identified. Additionally, we observed structural aberrations in chromosome 6 in 16/49 tumors (32.7%) across tumor types. In the pedHGG, H3-/IDH-wild-type subgroup TP53 alterations had a significant negative effect on OS. Conclusions Contrary to previous studies, our representative pediatric GC study provides evidence that GC has a strong predilection to arise on the background of specific molecular features (especially pedHGG_RTK2, pedHGG_A/B, EGFR and BCOR mutations, chromosome 6 rearrangements).