CD34 and glioblastoma: While we did not observe a significant relationship between density of CD34+ vessels and VM in primary glioblastoma, we did see a negative correlation between these vessel types in recurrent tumours, though this is potentially due to the reduction in endothelial vessel density at recurrence rather than the compensatory activity of tumour-derived vessels, as the correlation was relatively weak and the VM vessel density did not change significantly from primary tumours to recurrence.