No evidence for involvement of SDHD in neuroblastoma pathogenesis

BACKGROUND: Deletions in the long arm of chromosome 11 are observed in a subgroup of advanced stage neuroblastomas with poor outcome. The deleted region harbours the tumour suppressor gene SDHD that is frequently mutated in paraganglioma and pheochromocytoma, which are, like neuroblastoma, tumours originating from the neural crest. In this study, we sought for evidence for involvement of SDHD in neuroblastoma. METHODS: SDHD was investigated on the genome, transcriptome and proteome level using mutation screening, methylation specific PCR, real-time quantitative PCR based homozygous deletion screening and mRNA expression profiling, immunoblotting, functional protein analysis and ultrastructural imaging of the mitochondria. RESULTS: Analysis at the genomic level of 67 tumour samples and 37 cell lines revealed at least 2 bona-fide mutations in cell lines without allelic loss at 11q23: a 4bp-deletion causing skip of exon 3 resulting in a premature stop codon in cell line N206, and a Y93C mutation in cell line NMB located in a region affected by germline SDHD mutations causing hereditary paraganglioma. No evidence for hypermethylation of the SDHD promotor region was observed, nor could we detect homozygous deletions. Interestingly, SDHD mRNA expression was significantly reduced in SDHD mutated cell lines and cell lines with 11q allelic loss as compared to both cell lines without 11q allelic loss and normal foetal neuroblast cells. However, protein analyses and assessment of mitochondrial morphology presently do not provide clues as to the possible effect of reduced SDHD expression on the neuroblastoma tumour phenotype. CONCLUSIONS: Our study provides no indications for 2-hit involvement of SDHD in the pathogenesis of neuroblastoma. Also, although a haplo-insufficient mechanism for SDHD involvement in advanced stage neuroblastoma could be considered, the present data do not provide consistent evidence for this hypothesis

Lack of correlation between incidental ipsilateral subventricular zone radiation dose and overall survival in glioblastoma patients

BACKGROUND The role of the subventricular zone (SVZ) in glioblastoma (GBM) is controversial. The past decade, several retrospective studies were published concerning the potential correlation between incidental radiation of the SVZ and survival in GBM patients. Although these publications showed conflicting results, a large study claimed an overall survival (OS) benefit for GBM patients after gross total resection if the ipsilateral SVZ received a higher dose than 40 Gy. We investigated this finding in our own population of GBM patients. MATERIAL AND METHODS A multicenter retrospective study was conducted including all adult patients treated for histologically proven GBM from 2003–2014. All patients received 60 Gy radiation therapy after surgery and concomitant temozolomide. Exclusion criteria were: infratentorial GBM; presence of other neoplasm(s); known previous history of low grade glioma; incomplete radiotherapy data. Demographic data were collected from the patient charts. O6-methylguanin-DNA-methyltransferase-promotor-gene (MGMT) methylation was determined on stored tumor samples using semi quantitative methylation-specific polymerase chain reaction (qMSP). SVZs (ipsilateral, contralateral and bilateral) were contoured on radiotherapy treatment plans. Multivariate Cox regression analysis was used to study the correlation between incidental SVZ radiation dose and OS. Age (cut-off 65 years), Karnofsky Performance Score (KPS; cut-off 70), methylation of the MGMT-promotor gene and extent of resection (biopsy; subtotal resection, groos total resection) were used as covariates. Patients alive at time of database closure were censored for analysis. RESULTS 183 patients were eligible for analysis. Mean age at diagnosis was 62 years, with an average KPS of 70. In 34% of patients, gross total resection (GTR) was achieved, while in 28% only a biopsy was taken. MGMT-promoter gene methylation was present in 39% of cases. Median ipsilateral, contralateral and bilateral SVZ doses were 46.1 Gy, 25.35 Gy and 34.8 Gy resp. In multivariate Cox regression, all covariates (age, P = 0.011; KPS, P = 0.001; MGMT methylation, P = 0.000; extent of resection, P = 0.000) were significantly associated with OS. Mean OS was 23 months, but median OS 13 months. There was no correlation between incidental radiation dose of the ipsilateral SVZ and OS for 46 Gy or 40 Gy (hazard ratio 0.82 (0.6–1.1), P = 0.225 and 0.89 (0.63–1.23), P = 0.52 resp.) for the whole group nor for the subgroup of gross total resection. CONCLUSION In this group of GBM patients, age, KPS, extent of resection and methylation of the MGMT-promotor gene were significantly correlated with OS, but not incidental ipsilateral SVZ radiation dose. The previously published positive results may result from bias, possibly arising from lack of inclusion of MGMT-promotor gene methylation as an important independent prognostic factor