Sen. John McCain is discontinuing treatment for brain cancer — here's why glioblastoma is so deadly

It’s been just over a year since Sen. John McCain, a Republican from Arizona, was diagnosed with brain cancer, but the 81-year-old’s fight, according to his family, is officially coming to an end. “John has surpassed expectations for his survival,” reads a statement tweeted by his daughter Meghan McCain on Friday morning. “But the progress of disease and the inexorable advance of age render their verdict.”

The statement goes on to explain that McCain, “with his usual strength of will,” has opted to discontinue treatment of his aggressive cancer. “Our family is immensely grateful for the support and kindness of all his caregivers over the last year, and for the continuing outpouring of concern and affection from John’s many friends and associates, and the many thousands of people who are keeping him in their prayers,” the statement reads. “God bless and thank you all.”

Doctors first discovered McCain’s cancer while removing a blood clot from behind his eye last July and diagnosed him with primary glioblastoma. The Mayo Clinic defines glioblastoma as “an aggressive type of cancer that can occur in the brain or spinal cord” (in his case, “primary” refers to the brain).

Glioblastoma, also known as glioblastoma multiforme (GBM), can cause symptoms such as headaches, nausea, vomiting, and seizures but can go undetected for years. Vigorous chemotherapy and radiation are recommended, but even those who attack the cancer head-on face a grim prognosis. The one-year survival rate for GBM is 39 percent for wealthier patients and those under 70; the five-year survival rate is under 5.1 percent. According to one study from the Centers for Disease Control and Prevention, 90 percent of the 22,000 Americans diagnosed each year die within 24 months.

So what makes the cancer so deadly, and what does it mean when McCain says he’s stopping treatment? Andrew S. Chi, MD, chief of neuro-oncology and co-director of the brain tumor center at NYU Langone Health’s Perlmutter Cancer Center, is well-versed in the world of glioblastoma. He says there isn’t just one explanation for why the survival rate remains distressingly low.

“There are many reasons that it’s so deadly,” Chi tells Yahoo Lifestyle. “For one, it doesn’t grow as discrete masses. The cancer actually sends out infiltrating cells and fingers throughout the brain, so by the time you see a mass, you know there are cells in other parts of the brain that you can’t get out with surgery. The tumors are also characteristically very resistant to radiation, meaning we have to use much higher doses, and most of the chemotherapy we’ve tried have almost no activity. Even when they do they extend life, it’s only for a matter of months.”

On top of resistance to treatment, Chi says, the location of the cancer — the brain — is problematic. “The brain doesn’t have a lot of tolerance for tumor growing,” he says. “You can get a big tumor in the bone or the abdomen and only be mildly symptomatic. But a small tumor in the brain can cause tremendous problems — not only because it’s enclosed in a tight space, but because it controls language, thought, and all the other functions we have that make us human.”

Given how little can be done to stop the growth of the cancer — and how likely it is to come back — ending treatment is a call that many patients decide to make. “Almost always you reach a point where you decide to no longer do treatment; sometimes it’s because you finished the course, but more often it’s because the tumor is growing and the additional therapies haven’t worked,” he says. “The side effects of treatment can be severe, and some patients decide it no longer makes sense.”

Chi says that the length of life following the conclusion of treatment varies. If the tumors are continuing to grow, a patient may survive for only weeks; but if the tumor has simply entered an “observational” period, when it isn’t currently growing, then a person may live months or longer. “It’s one of the hardest decisions people make during the course of this disease,” Chi says. “There are people who survive a long time, but it’s an incredibly small percentage.”

Although it’s impossible to know what went into McCain’s decision, his family says they are thankful for the nation’s concern. “My family is deeply appreciative of all the love and generosity you have shown us during this past year,” Meghan McCain tweeted. “Thank you for all your continued support and prayers. We could not have made it this far without you — you’ve given us strength to carry on.”

Read more from Yahoo Lifestyle:

• A baby with a brain tumor underwent a miraculous recovery after a kiss from Pope Francis

• Cecile Richards, former Planned Parenthood president, says Trump administration is ‘putting politics ahead of the lives of women’

• ‘DWTS’ star Witney Carson on being diagnosed with melanoma at age 22

Follow us on Instagram, Facebook, and Twitter for nonstop inspiration delivered fresh to your feed, every day.