Introduction: Molecular heterogeneity in GBM is a novel area of research recently. As tumor infiltrating front in GBM is often left behind following tumor decompression, knowledge of its genetic makeup can improve the rationale of potential molecular targets.
Methods: MRI localised biopsies of the tumour core and PBZ were obtained from 25 Glioblastoma patients. The PBZ samples containing 15-30% tumour cells and core samples with predominantly tumour cells along with 8 non-neoplastic brain tissues were selected for a whole Genome Gene Expression Microarray. The list of differentially expressed genes between the tumour core and PBZ as compared to non-neoplastic brain tissue was identified using R Bioconductor. Selected genes were validated using Quantitative Real-Time PCR (qRT-PCR) and IHC.
Results: Unsupervised hierarchical clustering of the genes revealed that the tumour core and PBZ samples showed a varied gene expression profile and clustered into two distinct groups. Around 7123, 5188 and 991 genes were differentially expressed in Core versus Normal, PBZ versus Normal and PBZ versus Core. Novel genes like PBK (role in cell cycle), MELK (stem cell marker) and TOP2A (proliferation marker) were up-regulated in PBZ and tumour core as compared with normal brain and robustly validated on IHC. Pathways involved in cell cycle, immune response, cell-cell adhesion, cell-matrix interaction etc were commonly enriched in Periphery and tumour core compared to normal brain. Some of the novel markers were validated by Real time PCR and IHC.
Conclusions: We demonstrate that the key genes involved in tumour cell proliferation, invasion, migration, response to immune system and stemness markers are highly enriched in the PBZ. These genes, probably contribute to the resistance of PBZ cells to standard adjuvant therapy, resulting in tumour recurrence.
Patient Care: the study can identify novel molecules which can be potential therapeutic targets.
Learning Objectives: understand the molecular heterogeneity in GBM and infiltrating front, which can guide future research in target identification.