PO-338 Recurrent glioblastoma: a complex scenario dominated by loss of MMR proteins

Introduction Glioblastoma (GBM) is the most common primary brain tumour in adults and the Stupp protocol represents the standard of care. However, the tumour invariably relapses suggesting marked intra-tumour genetic heterogeneity enabling rapid adaptation to therapy. In-depth characterisation of recurrent GBM (rGBM) might contribute to better understand mechanisms behind tumour progression and enable rGBM treatment with targeted drugs. Material and methods Matched GBM samples have been collected at diagnosis and recurrence from adult patients (n=57) treated with the Stupp protocol. Expression of mismatch repair (MMR) proteins (MLH1, PMS2, MSH2, MSH6) was evaluated by IHC, followed by exome sequencing of 3 pairs showing loss of MSH6 reactivity as well as of 3 MSH6 positive pairs. In addition, established genetic and epigenetic markers of GBM were investigated along with their correlation with loss of MMR proteins and patients' survival. Results and discussions According to IHC results, 13 out of 52 rGBM samples (25%) lacked expression of MMR proteins. In particular, 11 among the 13 samples (85%) showed partial or total reduction of MSH6 expression. Conversely, almost all GBM samples at diagnosis (96.4%) stained positive for the 4 MMR markers. Consistent with IHC data, exome sequencing disclosed lack of variants in MMR genes in primary samples whereas rGBM samples lacking MSH6 expression were mutated in the abovementioned genes and shared a c.3438+1G>A* splicing variant in MSH6 with a potential loss of function effect. Moreover, MSH6 negative relapsed specimens were characterised by 30 to 100-fold more variants compared to the matched primary ones and lacked microsatellite instability. Notably, MMR deficiency was associated with significant telomere shortening. Conversely, the tumour pairs expressing MMR proteins showed an almost comparable number of mutations in primary versus relapsed samples and absence of variants in MMR genes both in the initial tumours and in their recurrent counterpart. Conclusion Our study shows that IHC staining is a valuable tool to identify a subset of rGBM patients with alterations in MMR genes linked to high mutational burden and, hence, potentially eligible for drugs targeting immune checkpoint inhibitors

MGMT promoter methylation in pediatric high-grade gliomas.

We read with great interest the recent articles of Buttarelli et al. [1] and Srivastava et al. [2] on MGMT status in pediatric high-grade gliomas. The authors observed MGMT promoter methylation in 7/24 (30%) and 10/20 (50%) of the tumors, respectively. In adults, MGMT promoter methylation is the most promising prognostic marker to predict patients' outcome and it has been observed in the 30\u201340% of the cases. On the other hand, only sporadic information are available regarding pediatric cases. In their seminal work, Donson and colleagues [3] observed four of ten (40%) GBM pediatric patients with methylation of the MGMT gene promoter and that the methylated cases were associated with an improved survival time. Moreover, MGMT down-regulation was associated with a good response to temozolomide therapy. Recently, Schlosser and colleagues demonstrated promoter methylation in 77% of pediatric high-grade gliomas [4]. To further investigate the role of MGMT promoter methylation status in this specific group of tumors, we retrospectively surveyed a series of ten pediatric patients surgically treated from January 2001 to September 2008, at the Department of Pediatrics (Pediatric Neurosurgery Unit) of the University Hospital of Padova (seven grade IV and three grade III gliomas). Patients included five males and five females with a mean age of 12.3 years (median 11.5 years) at diagnosis. In five cases, the surgical excision of the tumor mass was partial, in two cases sub-total and in three cases complete. All patients received post-operative chemotherapy with temozolomide (in seven cases combined with other alkylating agents) and radiation therapy. Overall, all patients suffered relapse or progression of the disease: three patients are still alive, whereas seven died. MGMT status assessment was performed as previously described [5], and no case of MGMT promoter methylation has been detected. This divergent data underlines the fact that we are still far from a well-defined characterization of pediatric cases. Further larger and multi-Institutional studies should investigate and validate the significant role of MGMT promoter methylation status assessment as a potential prognostic factor in pediatric high-grade gliomas, as well as to design different trials and treatment strategies for patients with unmethylated MGMT promoter

Intra-operative 5-aminolevulinic acid (ALA)-induced fluorescence of medulloblastoma: phenotypic variability and CD133(+) expression according to different fluorescence patterns.

5-Aminolevulinic acid (5-ALA) fluorescence has been proved advantageous in glioma surgery. Conflicting results have been reported by few studies published in literature about intra-operative 5-ALA-induced fluorescence of medulloblastoma (MDB). The aim of this study is to verify if these conflicting results could be explained by intra-tumoral histological and phenotypic differences. In the present case of a 45-year-old patient affected by a cerebellar MDB, histological analysis of cell phenotype and 5-ALA and CD133 correlation were performed in multiple samples according to different fluorescence patterns. Intra-operatively, the tumor appeared unevenly fluorescent under blue-violet light. Histologically, 5-ALA-intense biopsies from inner areas were characterized by a significant amount of cancer cells, whereas 5-ALA faint regions from peripheral areas displayed normal cerebellar features, with MDB cells infiltrating healthy tissues. Presenting our findings, we show the correlation between different 5-ALA fluorescence patterns of medulloblastoma with specific histological and phenotypical features. Thus, we hypothesize that a distinct relationship between CD133 expression and fluorescence accumulation presented in our study could partially explain the divergent results published in literatur

Non-anaplastic pleomorphic xanthoastrocytoma with neuroradiological evidences of leptomeningeal dissemination

CASE REPORT: A case of a non-anaplastic pleomorphic xanthoastrocytoma (PXA) presenting with leptomeningeal dissemination (LMD) affecting a 9-year-old girl is presented. DISCUSSION: The neoplasia in this young girl had the otherwise classical clinical features of PXA: the relatively advanced paediatric age of the patient, the seizures as presenting sign; the primary site in the temporal lobe; and the MRI findings of the partially solid and cystic superficial lesion. Only the tumour involvement of the chiasma and the infundibulus was a relatively unusual finding. In a 5-year period, the tumour underwent malignant transformation, bringing the child to death because of the primary tumour progression. However, the leptomeningeal deposits remained unchanged throughout the clinical course. CONCLUSION: To our knowledge, this is the first case of a non-anaplastic PXA presenting with disseminated disease. Thus, it was thought important to describe this case in order to add further information regarding the spectrum of the presenting clinical features of this rare neoplasm and the phenomenon of LMD of non-malignant glioma