John McCain has an aggressive kind of brain cancer that has a median survival rate of less than 15 months — here’s everything we know

Senator John McCain has been diagnosed with glioblastoma, an aggressive form of brain cancer. 

The diagnosis comes less than a week after McCain, who is 80, had brain surgery on Friday to remove a blood clot above his left eye. Once the clot was taken out, doctors determined that it was connected to brain cancer

The senator and his team of doctors at the Mayo Clinic in Arizona are reviewing treatment options, which could include radiation and chemotherapy. 

An aggressive brain cancer

Glioblastoma is the most commonly diagnosed form of brain cancer, though it’s still quite rare with only three cases per 100,000 people

The cancer tends to be treated with a combination of surgery to remove the tumour, radiation, and chemotherapy, according to the National Cancer Institute. The Mayo Clinic’s statement about McCain’s case did not mention surgery as one of the potential options for him (the procedure McCain had was just to remove the blood clot), though it’s unclear whether his doctors have ruled it out at this point.

With the combination of treatments, the median survival rate (a measure of how long patients on the treatment tend to survive) is 14.6 months, according to the American Brain Tumour Association. The ABTA noted that the five-year survival rate for glioblastoma, or per cent of people alive five years after their diagnosis, was just 10%. Children with glioblastoma tend to fare better than adults. 

McCain has a history of melanoma, which is considered the most serious form of skin cancer. However, his glioblastoma is unrelated to that. The Mayo Clinic noted in a statement that this is a primary tumour, meaning that it’s still in its original spot, rather than spreading around the body. 

Why brain tumours are tough to treat

Treating brain cancer is a very different process than treating cancer in any other part of the body because of the blood-brain barrier, which stops certain pathogens and molecules from passing from the blood into the brain. The blood-brain barrier is key to keeping the brain safe, but because it’s good at keeping things out, it’s also hard to get drugs like chemotherapy in. 

There’s also the challenge of tackling the mix of different cells that make up the tumour. 

“The cells don’t all behave the same way, so even when you kill some, the residual cells can take hold and grow again, so you’re fighting a constant uphill battle to get rid of every last cell,” Susan Chang, director of neuro-oncology at University of California San Francisco told Bloomberg

Advances in treatment

Former Vice President Joe Biden tweeted out his support for his friend, McCain, on Wednesday. Biden’s son Beau died in 2015 from brain cancer at 46. Biden subsequently launched a cancer moonshot initiative that’s brought him in contact with cancer doctors, researchers, and executives from around the world to discuss new treatment options for the disease.

There have been a number of medical advances in the treatment of cancer in the past few years. One major advance has been immunotherapy. Unlike chemotherapy, which involves administering powerful drugs that kill both cancerous and healthy cells (most healthy cells can repair themselves), immunotherapies harness the power of the immune system to help it identify and knock out just the cancerous cells. 

One type of immunotherapy, called checkpoint inhibitors, have seen a fair amount of success in treating melanoma, lung cancer, bladder cancer, and blood cancers.

Researchers are currently exploring whether these immunotherapies could also fight glioblastoma, though there have been some setbacks and cases where survival hasn’t improved.