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Simple Summary: Medulloblastoma is one of the most common malignant brain tumor types and comprises the molecular groups WNT-MB, SHH-MB TP53-wildtype, SHH-MB TP53-mutant and non-WNT/non-SHH MB. Developmental gene expression data suggest that these molecular groups arise from different sites of origin in the developing brain. Therefore, we hypothesized that intraoperative observation could enable the neurosurgeon to predict the molecular group during surgery and opt for a less aggressive resection in molecular groups with favorable prognosis to preserve neurological function. We reviewed the intraoperative reports, surgical videos and information on the molecular group of 58 patients who were operated at our institution from 1996 to 2020. Our data demonstrate that the correct prediction of the molecular group based on the intraoperatively observed site of origin was limited. Based on our results, we conclude that maximal safe resection should remain the aim of surgery irrespective of the observed site of origin. Developmental gene expression data from medulloblastoma (MB) suggest that WNT-MB originates from the region of the embryonic lower rhombic lip (LRL), whereas SHH-MB and non-WNT/non-SHH MB arise from cerebellar precursor matrix regions. This study aimed to analyze detailed intraoperative data with regard to the site of origin (STO) and compare these findings with the hypothesized regions of origin associated with the molecular group. A review of the institutional database identified 58 out of 72 pediatric patients who were operated for an MB at our department between 1996 and 2020 that had a detailed operative report and a surgical video as well as clinical and genetic classification data available for analysis. The STO was assessed based on intraoperative findings. Using the intraoperatively defined STO, "correct" prediction of molecular groups was feasible in 20% of WNT-MB, 60% of SHH-MB and 71% of non-WNT/non-SHH MB. The positive predictive values of the neurosurgical inspection to detect the molecular group were 0.21 (95% CI 0.08–0.48) for WNT-MB, 0.86 (95% CI 0.49–0.97) for SHH-MB and 0.73 (95% CI 0.57–0.85) for non-WNT/non-SHH MB. The present study demonstrated a limited predictive value of the intraoperatively observed STO for the prediction of the molecular group of MB. [ABSTRACT FROM AUTHOR]

Simple Summary: Ewing sarcoma is a rare pediatric tumor characterized by chromosomal translocations that give rise to aberrant chimeric transcription factors (e.g., EWSR1-FLI1). EWSR1-FLI1 defines a specific transcriptomic profile in Ewing sarcoma cells, which determines the tumorigenesis process. Our study focused on the identification of transcription factors regulated by EWSR1-FLI1. FEZF1 (FEZ family zinc finger protein 1), a transcription factor involved in neural cell identity, was identified as one of the most strongly upregulated genes by EWSR1-FLI1. Functional studies were carried out to characterize the involvement of FEZF1 in Ewing sarcoma pathogenesis. As a result, the inhibition of FEZF1 diminished clonogenicity and cell proliferation in three Ewing sarcoma cell lines. Transcriptomic analysis revealed several neural-specific genes transcriptionally regulated by FEZF1 and concomitantly regulated by EWSR1-FLI1, which could explain the neural-like phenotype observed in several Ewing sarcoma cell lines and tumors. Ewing sarcoma is a rare pediatric tumor characterized by chromosomal translocations that give rise to aberrant chimeric transcription factors (e.g., EWSR1-FLI1). EWSR1-FLI1 promotes a specific cellular transcriptional program. Therefore, the study of EWSR1-FLI1 target genes is important to identify critical pathways involved in Ewing sarcoma tumorigenesis. In this work, we focused on the transcription factors regulated by EWSR1-FLI1 in Ewing sarcoma. Transcriptomic analysis of the Ewing sarcoma cell line A673 indicated that one of the genes more strongly upregulated by EWSR1-FLI1 was FEZF1 (FEZ family zinc finger protein 1), a transcriptional repressor involved in neural cell identity. The functional characterization of FEZF1 was performed in three Ewing sarcoma cell lines (A673, SK-N-MC, SK-ES-1) through an shRNA-directed silencing approach. FEZF1 knockdown inhibited clonogenicity and cell proliferation. Finally, the analysis of the FEZF1-dependent expression profile in A673 cells showed several neural genes regulated by FEZF1 and concomitantly regulated by EWSR1-FLI1. In summary, FEZF1 is transcriptionally regulated by EWSR1-FLI1 in Ewing sarcoma cells and is involved in the regulation of neural-specific genes, which could explain the neural-like phenotype observed in several Ewing sarcoma tumors and cell lines. [ABSTRACT FROM AUTHOR]