By Makini Brice and Will Dunham

WASHINGTON (Reuters) - U.S. Senator John McCain, the maverick Republican who survived a Vietnam War prison camp and ran unsuccessfully for president, is discontinuing medical treatment for an aggressive form of brain cancer, his family said in a statement on Friday, a year after he announced his diagnosis.

"John has surpassed expectations for his survival," the family said, adding that the disease's progression and McCain's age, 81, have led him to stop treatment for the "aggressive glioblastoma."

"With his usual strength of will, he has now chosen to discontinue medical treatment," the family said.

McCain, who has represented Arizona in the Senate and House of Representatives for 35 years, has said the cancer was discovered in July 2017 and he has not been at the U.S. Capitol this year. He also had surgery for an intestinal infection in April.

McCain has had a reputation for speaking his mind, which led to a running feud with President Donald Trump. Sources close to McCain have said Trump would not be invited to the funeral.

The McCain-Trump relationship grew heated in 2015 when McCain said Trump's candidacy had "fired up the crazies." Trump retorted that the senator was "not a war hero" and referred to McCain's years as a prisoner of the North Vietnamese by saying: "I like people who weren't captured."

McCain castigated Trump last month for his summit with Russian President Vladimir Putin, issuing a statement that called their joint news conference "one of the most disgraceful performances by an American president in memory." He said Trump was "not only unable but unwilling to stand up to Putin."

McCain sought the Republican presidential nomination in 2000 but lost out to George W. Bush. He secured the nomination in 2008 but was defeated by Democratic nominee Barack Obama.

McCain has been known as a conservative and a foreign policy hawk with a traditional Republican view of world affairs. He has had a reputation for a hot temper and rarely shied away from a fight but has had Democratic fans who admired the way he could take a civil, bipartisan approach.

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McCain is the chairman of the Senate Armed Services Committee and his colleagues named the $716 billion defense policy bill for him. Trump did not mention McCain when he signed it earlier this month.

"Very sad to hear this morning’s update from the family of our dear friend @SenJohnMcCain," Republican Senate leader Mitch McConnell said on Twitter. "We are so fortunate to call him our friend and colleague. John, Cindy, and the entire McCain family are in our prayers at this incredibly difficult hour."

Former secretary of State John Kerry, a Democrat who served in the Senate with McCain, tweeted, "God bless John McCain, his family, and all who love him — a brave man showing us once again what the words grace and grit really mean."

McCain is the son and grandson of Navy admirals and after graduating from the U.S. Naval Academy became a fighter pilot during the Vietnam War. He was shot down during a bombing run over Hanoi and captured on Oct. 26, 1967. The crash and assault by his captors left him with two broken arms, a broken leg, broken shoulder and numerous stab wounds.

He spent the next 5-1/2 years in various prisons, including the notorious "Hanoi Hilton," where he was tortured and left with lasting disabilities.

McCain provided one of the most dramatic moments in recent Senate history in July 2017 when he voted against a Trump-backed bill that would have repealed the healthcare law pushed through by President Barack Obama.

The vote came late at night not long after McCain's diagnosis and he still bore a black eye and scar from the surgery when he gave an emphatic thumbs-down gesture to scuttle the measure.

Trump was furious about McCain's vote and frequently referred to it at rallies but without mentioning McCain by name.

McCain was elected to the House in 1982 and after two terms was elected to the Senate to replace retiring conservative leader Barry Goldwater.

(Corrects number of House terms to two in final paragraph)

(Reporting by Timothy Ahmann and Makini Brice; Writing by Bill Trott and Will Dunham; Editing by Jonathan Oatis and Jeffrey Benkoe)