Sen. John McCain has decided to discontinue medical treatment in his battle with brain cancer, his family said in a statement Friday. The Arizona Republican senator's family said McCain has "surpassed expectations for survival," but the "progress of disease and the inexorable advance of age render their verdict." McCain, 81, was diagnosed with glioblastoma more than a year ago.

"Last summer, Senator John McCain shared with Americans the news our family already knew: he had been diagnosed with an aggressive glioblastoma, and the prognosis was serious," McCain's family said in a statement. "In the year since, John has surpassed expectations for his survival."

"But the progress of disease and the inexorable advance of age render their verdict," the family statement continued. "With his usual strength of will, he has now chosen to discontinue medical treatment. 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. God bless and thank you all."

McCain, a war hero, was first elected to the Senate in 1986.

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McCain's diagnosis was first announced in July 2017. His wife, Cindy, tweeted about her love for her husband of 38 years and her appreciation for everyone who has come alongside them in the last year.

I love my husband with all of my heart. God bless everyone who has cared for my husband along this journey. pic.twitter.com/v27sEbboii — Cindy McCain (@cindymccain) August 24, 2018

Meghan McCain, their daughter, said her family wouldn't have made it this far without the support of others.

"My family is deeply appreciative of all the love and generosity you have shown us during this past year," she 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."

My family is deeply appreciative of all the love and generosity you have shown us during this past year. 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. pic.twitter.com/KuAQSASoa7 — Meghan McCain (@MeghanMcCain) August 24, 2018

Sen. Lindsey Graham, perhaps McCain's closest friend in the Senate, praised the McCain family, saying in a statement, "I just want to acknowledge the continuing and abiding love, care, and dedication that Cindy McCain and the family are providing John.

"Cindy remains steadfast and is traveling every step of the way on this difficult journey with John. The love provided by Meghan and the McCain children to their father has been comforting to witness. The entire McCain clan is doing exactly what the McCains have done through generations — rise to the meet the challenge."

He went on to say, "Above all else, I know John wants his family, friends and staff to understand how much he appreciates their love, care, and kindness."

Senate Majority Leader Mitch McConnell, who has worked with McCain for years in the Senate, said he was saddened to learn the news.

"Very sad to hear this morning's update from the family of our dear friend @SenJohnMcCain," McConnell tweeted. "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."

Very sad to hear this morning’s update from the family of our dear friend @SenJohnMcCain. 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. — Leader McConnell (@SenateMajLdr) August 24, 2018

Speaker of the House Paul Ryan said McCain "personifies service to our country."

John McCain personifies service to our country. The whole House is keeping John and his family in our prayers during this time. — Paul Ryan (@SpeakerRyan) August 24, 2018

Through his years in the Senate, McCain, known as the maverick, established a reputation as someone never afraid to speak his mind.

McCain has spent some of the last year in the Senate standing up to the president, and his own party, when he has deemed necessary. McCain voted against the Republican-led effort to repeal Obamacare last year, and has spoken out strongly against Mr. Trump's relationship with Russian President Vladimir Putin.

After his diagnosis last year, McCain returned to the Senate floor to give a rousing speech to his colleagues, urging them to return to "regular order," fight for principles, and rise above party politics.

"Our responsibilities are important, vitally important, to the continued success of our republic," he said on the Senate floor at the time. "And our arcane rules and customs are deliberately intended to require broad cooperation to function well at all," he said. "The most revered members of this institution accepted the necessity of compromise in order to make incremental progress on solving America's problems and defend her from her adversaries."