A childhood brain cancer that often spreads may do so because the secondary tumours differ genetically from the original growth, say researchers who suggest a different treatment approach is needed.

Medulloblastoma is rare and can be cured in about 60 per cent of cases, but the aggressive radiation and chemotherapy to the developing brain and spinal cord can cause permanent damage to the nervous system.

Researchers can start working on developing treatment plans that will kill the cancer cells in both the primary and the metastatic tumours, says Dr. Michael Taylor. (Hospital for Sick Children/Canadian Press)

Now researchers at the Hospital for Sick Children in Toronto and their colleagues in Montreal, the U.S., Germany, U.K. and the Netherlands have found genetic differences between the primary tumour and the metastases or little tumours that spread from the main one.

"Now that we know we are treating a single cancer with two distinct populations, each with their own distinct genetic profiles, we can work on developing treatment plans that will kill the cancer cells in both the primary and the metastatic tumours," said Dr. Michael Taylor, who led the research team at Sick Kids.

Previously, scientists assumed that cancer spread in medulloblastoma when cells randomly moved. The new findings show that metastases result from a small set of cells that escape from the first tumour and spread in the brain or spinal cord.

In the study, the researchers found new mutations in medulloblastoma mouse models and metastatic tumours from seven human patients.

The findings suggest that doctors should biopsy the metastases as well as the primary tumour, which isn't normally done now.

Routine biopsy and analysis of human metastases will be essential to find out which mutations drive tumour development and to find which occur frequently enough to pursue as targets for treatments, Steven Clifford of the Northern Institute for cancer Research at Newcastle University in the U.K. said in a journal commentary published with the study.

The study was funded by the Canadian Cancer Society, Sick Kids Foundation, Brainchild and the Pediatric Brain Tumour Foundation.