(CNN) -- Sen. John McCain, who was diagnosed with brain cancer last year, has made the decision to discontinue medical treatment, his family said in a statement on Friday.
"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. 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. With his usual strength of will, he has now chosen to discontinue medical treatment," the family of the Arizona Republican said in a statement.
McCain, the 2008 Republican presidential nominee, is a key voice in the Republican Party and an icon of the Senate.
The statement went on to say, "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's wife and daughter both put out additional statements on Twitter.
Cindy McCain, the senator's wife, wrote in a tweet, "I love my husband with all of my heart. God bless everyone who has cared for my husband along this journey."
The senator's daughter, Meghan McCain, said in a tweet, "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."