John McCain reveals he has a 'very poor prognosis' — here's what we know about his aggressive form of brain cancer

Sen. John McCain of Arizona has glioblastoma, an aggressive form of brain cancer.

McCain, who is 81, had brain surgery in July to remove a blood clot above his left eye. His doctors determined the clot was connected to brain cancer. Shortly after, McCain returned to Washington to dramatically vote down the GOP's healthcare bill, before returning to Arizona for treatment.

McCain told CBS News' "60 Minutes" that doctors are treating the brain cancer with radiation and chemotherapy. While the prognosis is never good for glioblastoma, McCain's perspective is positive. 

RELATED: Reactions to Senator John McCain's brain tumor diagnosis

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Reaction to Senator John McCain's brain tumor diagnosis
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Reaction to Senator John McCain's brain tumor diagnosis
Statement regarding my father @SenJohnMcCain: https://t.co/SMte9Hkwkq
@MeghanMcCain Her words are extraordinary. https://t.co/nikKbSxTLE
Melania and I send our thoughts and prayers to Senator McCain, Cindy, and their entire family. https://t.co/SO4XYgnyug
John McCain is an American hero & one of the bravest fighters I've ever known. Cancer doesn't know what it's up against. Give it hell, John.
Karen & I are praying for @SenJohnMcCain. Cancer picked on the wrong guy. John McCain is a fighter & he'll win this fight too. God bless!
John McCain is as tough as they come. Thinking of John, Cindy, their wonderful children, & their whole family tonight.
.@SenJohnMcCain is a hero to our Conference and a hero to our country. https://t.co/Ld2lQH1mMn
I love @SenJohnMcCain. Unbeatable, unbreakable. He's Teddy Roosevelt's "man in the arena" even when we're on opposi… https://t.co/rkLNj5ToVL
Praying for my friend @SenJohnMcCain, one of the toughest people I know.
John and I have been friends for 40 years. He's gotten through so much difficulty with so much grace. He is strong - and he will beat this.
.@SenJohnMcCain is an American hero. I pray for him and his family. I look forward to seeing him soon.
.@SenJohnMcCain is a hero, a patriot and a fighter. I am privileged to call him a friend. Paul & I pray for his recovery and his family.
.@SenJohnMcCain has always been a warrior. It's who he is. All of us, not as Republicans or Democrats, but as Ameri… https://t.co/wIJTj8tdY7
My friend @SenJohnMcCain is a dogged ole S.O.B. Sharp as hell and tougher than a $2 steak. I look forward to catching up with him soon.
Heidi and I are lifting up @SenJohnMcCain in prayer. He's an American hero who fought, bled, and suffered for our Nation. A true patriot.
As he’s shown his entire life, don’t bet against John McCain. Best wishes to him for a swift recovery.
If there is anyone who knows how to fight against the challenges life throws at us, it's @SenJohnMcCain. Prayers for a speedy recovery.
John McCain is a hero, one of the most respected senators and a friend. The hopes and prayers of the nation are with him and his family.
Hang in there @SenJohnMcCain. You're tough! You can beat this. Fight, fight, fight! I am proud to call you my friend.
Just spoke to @SenJohnMcCain. Tough diagnosis, but even tougher man.
Thinking about a hero, my Chairman, my friend John McCain. Stay strong!
John McCain is one tough fighter - we know he'll face this diagnosis with courage and strength. Our family... https://t.co/XXTUltNGey
Praying for @SenJohnMcCain and his family tonight. You won't meet any stronger and braver than him.
If anyone can survive brain cancer it's @SenJohnMcCain - NH loves you. #hero #fighter #survivor #nhpolitics
J.McCain will be around for a long while. I've always known he'd outlive me. I wrote the eulogy he'll give at my funeral. It's very touching
My thoughts and prayers are with @SenJohnMcCain tonight, his wife @cindymccain and the entire family. Join me in saying a prayer for them.
Hatch statement on @SenJohnMcCain. https://t.co/yG7vi0IGfi
Praying for Senator McCain and his family. https://t.co/f4tcusDWKl
Thinking of Sen McCain and his family tonight. Was so honored to visit the infamous "Hanoi Hilton" with him a few w… https://t.co/XdUust5lBT
John McCain is an American hero and a relentless fighter. I wish him Godspeed in this fight and look fwd to welcoming him back to work soon.
.@SenJohnMcCain our prayers for your recovery and comfort to your family. I have been on @FightBrainTumor board for 14 yrs. We fight on. . .
So sad about @SenJohnMcCain, Lion of the Senate. He's a man of incredible strength & courage-qualities I hope will once again see him thru.
Very sad to hear that @SenJohnMcCain has been diagnosed w/ brain cancer. He's a fighter & a true patriot. Praying that he gets better soon.
Keep @SenJohnMcCain, Cindy, and his family in your thoughts and prayers. He's a fighter, and we hope to see him back in the Senate soon.
My thoughts and prayers are with you @SenJohnMcCain, a true American hero and dedicated public servant.
So sad to hear the heartbreaking news about my friend @SenJohnMcCain. My prayers are w/ the McCain family and w/ John, a true fighter.
I love John McCain. I've traveled with him, I've been tongue lashed by him, I've worked with him, and I wish I could be with him tonight.
Hey John! We can't wait to welcome you to the club. You got this! ❤️@SenJohnMcCain #cancersurvivors
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"They said that it's very serious. That the prognosis is very, very serious," McCain told 60 Minutes. "Some say three percent, some say 14 percent. You know, it's a very poor prognosis. So I just said, 'I understand. Now we're gonna do what we can, get the best doctors we can find and do the best we can.' And, at the same time, celebrate with gratitude a life well lived."

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 tumor, radiation, and chemotherapy, according to the National Cancer Institute. McCain had surgery to remove the initial blood clot and is now being treated with radiation and chemotherapy while continuing to work. 

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 Tumor Association. The ABTA noted that the five-year survival rate for glioblastoma, or the percentage of people alive five years after receiving the diagnosis, was just 10%. Children with glioblastoma tend to fare better than adults.

RELATED: John McCain through the years

20 PHOTOS
John McCain through the years
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John McCain through the years
UNITED STATES - FEBRUARY 27: TV RATINGS--Senate Commerce Committee Chairman John McCain, R-Ariz., during hearing on the TV ratings system. (Photo by Douglas Graham/Congressional Quarterly/Getty Images)
20th August 1992: The Republican Senator from Arizona, John McCain, speaking at the Republican National Convention. A fomer prisoner of war for several years in Vietnam, he contested his party's nomination for the 2000 election. (Photo by Consolidated News Pictures/Getty Images)
HANOI, VIET NAM: U.S. Sen. John McCain, a former POW, looks 31 May 1993 at a display of personal belongings of American POWs at the joint POW/MIA archives center in the Hanoi Army Museum. McCain is with U.S. Sen. John Kerry and a delegation on a two-day visit aimed at obtaining more access to archives dealing with the fate of missing U.S. servicemen. (Photo credit should read HOANG DINH NAM/AFP/Getty Images)
UNITED STATES - MAY 18: MCCAIN'S DAY--Sen John McCain, R-Ariz., relaxes in his office at about 2:15 p.m. (Photo by Scott J. Ferrell/Congressional Quarterly/Getty Images)
UNITED STATES - JUNE 02: McCAIN BILL--John McCain,R-Ariz.,during a press conference on the McCain Bill and tobacco legislation. (Photo by Douglas Graham/Congressional Quarterly/Getty Images)
WASHINGTON, : US Senator John McCain, R-AZ, chairman of the Senate Committee on Commerce, Science and Transportation begins the start of a hearing on the investigation of the scandal surrounding the 2002 Salt Lake City Winter Olympics on Capitol Hill in Washington, DC 14 April, 1999. AFP PHOTO/Mario TAMA (Photo credit should read MARIO TAMA/AFP/Getty Images)
HANOVER, : US Senator John McCain speaks to reporters 27 October,1999 in Hanover, New Hampshire. McCain criticized sugar, oil, and corn (shown behind) subsidies and linked them to 'soft money' campaign contributions. (ELECTRONIC IMAGE) AFP PHOTO Luke FRAZZA (Photo credit should read LUKE FRAZZA/AFP/Getty Images)
MANCHESTER, : Republican president hopeful John McCain greets supporters as he arrives at a debate forum sponsored by a local television station 02 December, 1999, in Manchester, New Hampshire. McCain will debate the other Republican candidates seeking the party's presidential nomination. (DIGITAL IMAGE) AFP PHOTO/John MOTTERN (Photo credit should read JOHN MOTTERN/AFP/Getty Images)
UNITED STATES - CIRCA 2000: John McCain addresses a shadow convention at the Annenberg Center of the University of Pennsylvania. McCain was booed when he asked suppoters to back his former primary opponent, George W. Bush. The shadow convention was put on near the site of the Republican National Convention in Philadelphia to highlight issues that the organizers say the major parties are ignoring. (Photo by Harry Hamburg/NY Daily News Archive via Getty Images)
CAMDEN, UNITED STATES: GOP presidential hopeful US Senator John McCain (R-AZ) waves during an 'Old Fashion BBQ and Stump Meeting' on the front yard of a supporter's house 08 January 2000 in Camden, South Carolina. (ELECTRONIC IMAGE) AFP PHOTO/Paul J. RICHARDS (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images)
PETERBOROUGH, NH - JANUARY 30: Republican presidential hopeful Sen. John McCain (L) and his wife Cindy are showered with confetti following McCain's final town meeting 30 January, 2000 in Peterborough, New Hampshire. (ELECTRONIC IMAGE) (Photo credit should read C.J. GUNTHER/AFP/Getty Images)
GREENWOOD, : Republican presidential hopeful John McCain makes a point 14 February 2000 during a town hall meeting at the American Legion Post 20 in Greenwood, South Carolina. McCain is campaigning heavily in the southern state against Texas Governor Geroge W. Bush ahead of the 19 February 2000 primary. (ELECTRONIC IMAGE) AFP PHOTO/Tim SLOAN (Photo credit should read TIM SLOAN/AFP/Getty Images)
THE TONIGHT SHOW WITH JAY LENO -- Episode 1789 -- Pictured: (l-r) Senator John McCain during an interview with host Jay Leno on March 1, 2000 -- (Photo by: Paul Drinkwater/NBC/NBCU Photo Bank via Getty Images)
UNITED STATES - APRIL 30: Sen. John McCain, R-AZ, at a Senate Commerce, Science and Transportation Committee hearing on climate change. (Photo By Tom Williams/Roll Call/Getty Images)
UNITED STATES - FEBRUARY 12: TEMPORARY GUEST WORKERS--Witness Sen. John McCain, R-Ariz., during the Senate Judiciary Immigration, Border Security and Citizenship Subcommittee hearing titled 'Evaluating a Temporary Guest Worker Proposal.' (Photo by Scott J. Ferrell/Congressional Quarterly/Getty Images)
UNITED STATES - JUNE 28: SENATE POLICY LUNCHES--Sen. John McCain, R-Ariz., talks to reporters after the Senate GOP policy luncheon. (Photo by Scott J. Ferrell/Congressional Quarterly/Getty Images)
WASHINGTON - SEPTEMBER 20: U.S. Senator John McCain (R-AZ) addresses The Northern Virginia Technology Council's Titans breakfast at the Capitol Hilton September 20, 2006 in Washington, DC. McCain spoke on a variety of subjects, including telecommunications legislation, net neutrality, research and development tax credits, immigration, and Internet taxes. He also addressed the rift that he and several other Republican senators are having with the White House over the Geneva Conventions. (Photo by Chip Somodevilla/Getty Images)
KABUL, AFGHANISTAN - JULY 04: US Senator John McCain (C) holds a press conference at ISAF HQ in Kabul, Afghanistan on July 4, 2017. US Senator John McCain visited the headquarters of NATO-led mission after his visit at Pakistan. (Photo by Haroon Sabawoon/Anadolu Agency/Getty Images)
WASHINGTON, July 13, 2017 -- U.S. Senator John McCain is swarmed by reporters as he leaves a meeting on Capitol Hill in Washington D.C. July 13, 2017. Senate Republicans of the U.S. Congress on Thursday unveiled a new healthcare bill that they hoped can fulfill their long-time goal to 'repeal and replace' the Affordable Care Act. (Xinhua/Ting Shen via Getty Images)
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Why brain tumors are tough to treat

Treating brain cancer is very different from 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 tumor.

"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, the director of neuro-oncology at the University of California at San Francisco, told Bloomberg in July.

Advances in treatment

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

There have been numerous 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. It doesn't appear that McCain is using these approaches for now. 

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

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

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