The family of Sen. John McCain said in a statement Friday that the Arizona Republican has decided to discontinue medical treatment after he was diagnosed last year with an aggressive form of brain cancer.

McCain, 81, revealed last summer that he had been diagnosed with primary glioblastoma.

“John has surpassed expectations for his survival,” the McCain family said in a statement. “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.”

Members of the McCain family shared the statement Friday on social media.

“I love my husband with all of my heart,” John McCain’s wife, Cindy McCain, wrote in a Twitter post that included the statement. “God bless everyone who has cared for my husband along this journey.”

John McCain's daughter, Meghan McCain, thanked supporters in a separate post on Twitter.

"We could not have made it this far without you," she wrote. "You've given us strength to carry on."

Politicians reacted to the news with well-wishes for McCain, who has been been away from the Capital since December.

Doctors discovered John McCain’s brain tumor after he underwent surgery in July 2017 to remove a blood clot from above his eye. He was previously diagnosed with melanoma in 1993, 2000 and 2002, and underwent treatment each time. Those cancers did not spread, according to John McCain’s doctors.

>> Related: Photos: Sen. John McCain through the years

Glioblastoma is a particularly aggressive form of cancer and the prognosis is often poor, according to the American Brain Tumor Association. The average survival rate for patients with malignant glioblastoma is around 14 months if the person gets treatment. Around 10 percent of patients with the disease live for five years or longer.