An international team has found that medulloblastomas, a brain tumour that occurs most often in children, originates from two types of cell -- multipotent neural stem cells (NSCs) and granule neuron precursors (GNPs).

NSCs are stem cells that can become most types of cell within the nervous system while GNPs are similar to stem cells but give rise to a type of cells called granule neurons.

“There was good evidence that either cell type could be the origin of medulloblastomas, but no one considered that both sets of evidence could be correct, and that these tumours could actually begin in two different cell types.

“Identifying the normal cell that gives rise to a tumour is important because it allows direct comparisons between tumour cells and their normal counterparts so that key differences and vulnerabilities in tumour can be identified.

“Also, recent studies suggest that cells resembling the original cell may persist in mature tumours and can be critical in ensuring its survival. If so, these cells would be an excellent target for treatment,” lead scientist Brandon Wainwright was quoted by the ‘Cancer Cell’ journal as saying.

Wainwright of Queensland University and colleagues at Duke University in the United States made their discovery by examining a gene called Patched which is involved in the regulation of both neural stem cells and GNPs. When the gene is inactivated, medulloblastomas develop.

However, when inactivation occurs, it happens in all cells, so there was no way of knowing in which cell the tumour had begun.

The team took advantage of an allele, or version, of Patched that allows inactivation of the gene in either GNPs or neural stem cells, and found that the tumours developed no matter in which cell Patched was inactivated.

The study could also have wider implications for treating other types of cancer, as the team also found that cancer doesn’t always originate in the same way.

“It has always been thought that cells had to mutate several times before becoming a tumour. In this study we found that some stem cells only needed to mutate once.