TORONTO - A new study is shedding light on why treatment often fails when a devastating form of pediatric brain cancer spreads.

The cancer is called medulloblastoma; it is rare and can be cured in about six out of 10 cases, but treatment for it profoundly changes the lives of the kids who develop it.

Treatment is aggressive and involves radiation of the brain and spine, which has permanent physical and cognitive consequences.

Research led by experts at Toronto's Hospital for Sick Children has found that the little tumours that spread from the main tumour in this form of cancer are genetically different from the main tumour.

Senior author Dr. Michael Taylor says that explains why current treatments fail to kill the small secondary tumours.

The study, published in the journal Nature, says in order to be successful, therapies that target both the main tumour and the secondary tumours will be needed.