Tumour that took Downie

Photo: The Canadian Press

The death of Canadian singer-songwriter Gord Downie from glioblastoma is a grim reminder of the daunting nature of the invasive brain tumour, which has one of the poorest survival rates of any cancer.

And, say scientists and brain tumour patient advocacy groups, his passing also focuses a spotlight on the need for more funding for research into the deadly cancer — a charitable cause the Tragically Hip frontman and his bandmates championed after his diagnosis was publicly disclosed in May 2016.

The exact cause of glioblastoma multiforme — so called because it contains various cell types — is unknown, but research increasingly suggests that genetic mutations give rise to the highly aggressive tumour.

About 1,000 Canadians are diagnosed each year with a glioblastoma and only about four per cent of those patients survive five years or longer. The average period of survival following diagnosis is about 18 months.

GBMs, as they're sometimes called, occur more often in men than in women and increase in frequency with age. Those most affected are adults aged 45 to 75; GBMs make up only three per cent of childhood brain tumours.

What makes a glioblastoma so difficult to treat is that as the tumour grows, it sends out finger-like tentacles that worm their way into surrounding brain tissue.

"It's embedded in the brain and it infiltrates into the brain in places where you just can't remove it," says neurosurgeon Dr. Peter Dirks, a senior scientist in brain tumour research at Toronto's Hospital for Sick Children.

"We have the challenge that parts of your brain are essential for function, even the essence of who we are and how we communicate and how we laugh at jokes," he says. "We don't want to remove or harm those areas that are essential for us to function and make us the people who we are."

While surgery may remove the bulk of a tumour, there are often areas of the brain that can't safely be reached. Those more remote areas may harbour residual cancer cells that can spark recurrence of the cancer, despite treatment with radiation and chemotherapy.

"The tumours still have a habit of coming back, even if you thought you got it all, because there's still a few cells left that have been crawling deeper into the brain that have the capacity to multiply and cause the tumours to regrow," Dirks says.

Another reason they are so tough to eliminate, he says, is that many chemotherapy agents are unable to cross the blood-brain barrier, stopping them from attacking cancer cells within the brain.

The biggest advance in the last 10 years was the development of temozolomide, a chemotherapy drug that has the ability to penetrate the blood-brain barrier. A subset of glioblastoma patients respond somewhat to the medication, prolonging their survival a little bit longer, says Dirks.

"But many, many patients don't respond at all," he says. "It's not like there's really a therapy that we can tell people, 'Well, this at least will definitely slow it down or put you into remission.'"