Researchers identify two-tier system in brain tumours
An international team of researchers has discovered that the second most common type of malignant brain tumour in children is ependymomas. The finding is part of a large molecular-genetic study of ependymomas of the cerebellum. Presented in the journal Cancer Cell, the study reveals that based on the anomalies of their genetic material, ependymomas of the cerebellum are classified in two distinct subgroups: group A ependymomas, and group B ependymomas. The former assume negative characteristics while the latter have a positive prognosis.
Ependymoma emerges from precursor cells of the central nervous system tissue that lines the hollow cavities of the brain. Treatments to fight this tumour have varying results. Some patients' conditions are improved by surgery and radiotherapy, which help stop the tumour from growing, while others suffer from a disease that moves quickly and severely. Around 50% of children contend with tumours that continue to grow, and some of them die from it.
'It is the patients with a severe course, in particular, who urgently need better therapies,' explains Dr Stefan Pfister, a researcher at the German Cancer Research Center (DKFZ) and Heidelberg University Hospitals, who cooperated with colleagues from Canada, Italy, Poland, Russia and the United States.
The team assessed the activity of individual genes in 583 tissue samples. They investigated the genetic material for losses or gains of whole deoxyribonucleic acid (DNA) segments. The researchers performed independent assessments of the two tumour groups; the results were then validated on the tissue samples of a third group. According to the team, doing this enabled them to obtain valuable results.
They point out that group A tumours have relatively few losses or gains of gene segments. But a number of genes that influence key cancer signalling pathways are activated. On the one hand, group A tumours often metastasise and patients usually die. Group B tumours, on the other hand, offer more hope to patients despite the fact that the genome of these cancer cells is not very stable. Experts say typical characteristics are gains of large segments of chromosomes 9, 15 and 18, and losses of chromosomes 6 and 22.
'The genetic differences between these two types are so marked that we have to speak of two different diseases that may even arise from different original cells,' Dr Pfister says.
The German group plans to investigate this matter further. They will assess group A ependymomas to find out which of the genetic alterations are so-called driver mutations, the mutations that trigger the production of cancer cells. Further work will help researchers identify potential targets for improved drugs capable of fighting group A tumours.
It should be noted that researchers have already developed targeted drugs for a number of signalling pathways that are hyperactive in group A ependymomas. Clinical trials are now testing these drugs for other cancer types. The team says it is likely that several of these substances could be viable for treatment against ependymomas.