MBRS-51. MUTATIONS IN BRPF1 FOUND IN SHH MEDULLOBLASTOMA PREVENT INTERACTION WITH TP53 AND LEADS TO RADIORESISTANCE IN VITRO

Medulloblastoma (MB) is one of the most common pediatric tumors in children. Among them, SHH subgroups of MB (MB_SHH) is characterized by constitutive activation of SHH pathway. Somatic mutations in BRPF1, a chromatin modifier, is found in more than 5% of MB_SHH and accounts for almost 20% of adult MB_SHH but its potential role in MB_SHH pathophysiology is still unknown. In this study, we first examined the function of Brpf1 on pro-tumorigenic features of MB_SHH and evaluated molecular pathways regulated by Brpf1 using Brpf1floxed::Atoh1-Cre conditional knockout mice, in which Brpf1 is conditionally deleted in cerebellar granule neuron progenitors (GNPs). While RNA-seq analysis on GNPs from Brpf1 WT and KO mice showed significant differences in the pathways related with cell cycle and cell death, deletion of Brpf1 did not cause acceleration of tumorigenesis in the Ptch1 heterozygous tumor-prone. Background: Co-immunoprecipitation followed by mass spectrometry analysis identified interaction partners of BRPF1 including MOZ, MORF and ING5, known partners of BRPF1. Gene ontology analysis also depicted pathways important for cell cycle progression, cell death and response to DNA damage. Consistent with these observations, TP53 was identified as a novel co-factor of BRPF1. Of note, some of MB_SHH-relevant BRPF1 mutations prevented interaction with TP53. According to the previous finding that cytosolic TP53 is required for apoptotic cell death, GNPs expressing the BRPF1-R600X mutant gene exhibited the resistance to irradiation-induced cell death. In conclusion, our data revealed that BRPF1 mutants found in MB_SHH could prevent the complex formation with TP53, leading to enhanced resistance to cell apoptosis.

Hydrocephalus in children with ruptured cerebral arteriovenous malformation

OBJECTIVE

Hydrocephalus is a strong determinant of poor neurological outcome after intracerebral hemorrhage (ICH). In children, ruptured brain arteriovenous malformations (bAVMs) are the dominant cause of ICH. In a large prospective cohort of pediatric patients with ruptured bAVMs, the authors analyzed the rates and predictive factors of hydrocephalus requiring acute external ventricular drainage (EVD) or ventriculoperitoneal shunt (VPS).

METHODS

The authors performed a single-center retrospective analysis of the data from a prospectively maintained database of children admitted for a ruptured bAVM since 2002. Admission clinical and imaging predictors of EVD and VPS placement were analyzed using univariate and multivariate statistical models.

RESULTS

Among 114 patients (mean age 9.8 years) with 125 distinct ICHs due to ruptured bAVM, EVD and VPS were placed for 55/125 (44%) hemorrhagic events and 5/114 patients (4.4%), respectively. A multivariate nominal logistic regression model identified low initial Glasgow Coma Scale (iGCS) score, hydrocephalus on initial CT scan, the presence of intraventicular hemorrhage (IVH), and higher modified Graeb Scale (mGS) score as strongly associated with subsequent need for EVD (all p < 0.001). All children who needed a VPS had initial hydrocephalus requiring EVD and tended to have higher mGS scores.

CONCLUSIONS

In a large cohort of pediatric patients with ruptured bAVM, almost half of the patients required EVD and 4.4% required permanent VPS. Use of a low iGCS score and a semiquantitative mGS score as indicators of the IVH burden may be helpful for decision making in the emergency setting and thus improve treatment.

P14.99 Clinical and biologic features predictive of survival after relapse of childhood medulloblastoma

BACKGROUND

Salvage therapy for recurrent medulloblastoma (MB) is not standardized. Factors associated with survival after recurrence have not been reported.

MATERIAL AND METHODS

Medical records were reviewed for 155 consecutive patients with newly diagnosed MB between 2007 and 2017, treated at Gustave Roussy and Hospital Necker. The following variables were collected for all patients: age at diagnosis, stage, histology (central review according to WHO 2016 classification), molecular subgrouping (DNA methylation), first-line treatment modalities, time to relapse, pattern of recurrence and current status.

RESULTS

A disease recurrence was observed in 47 patients (30%) at a median time of 15 months (range, 1–88 months). The 1-year survival after recurrence was 44% (CI 95%,29.6 to 58.8). The pattern of recurrence was local in 9 patients, metastatic in 21 and combined local and metastatic in 17 patients. The time to first recurrence, less or more than 12 months from diagnosis, was a predictor of post-recurrence overall survival (p < 0.0001) after adjustment for age, treatment, MYC amplification and molecular subgroups. Twenty-seven patients (57%) experiencing recurrent or progressive disease more than 12 months after diagnosis, had an estimated 1-year survival after recurrence of 100% (CI 95%, 100.0 to 100.0) vs 30% (CI 95%, 12.2 to 50.1) with an earlier recurrence. Early relapse was more frequent in children younger than 5 years of age at diagnosis (75% vs 37%, p =0.009), anaplastic/large cell MB (30% vs 3.7%, p=0.046) and Group 3 tumours (76.5% vs 20.8%, p=0.003). Other factors influencing post-relapse survival were metastatic disease and treatment modalities at diagnosis. Multivariable analyses will be presented.

CONCLUSION

The overall prognosis after relapse remains poor. Time to relapse is a significant prognostic factor for postrelapse survival and may help in the design of clinical trials evaluating new agents.