Sen. John McCain (R-Ariz.) has been diagnosed with brain cancer, the Mayo Clinic Hospital in Phoenix said Wednesday.

The tumor was discovered after the senior Arizona senator underwent a minor procedure last week to remove a blood clot from above his left eye.

"Subsequent tissue pathology revealed that a primary brain tumor known as a glioblastoma was associated with the blood clot," the hospital said in a statement.

"The Senator and his family are reviewing further treatment options with his Mayo Clinic care team. Treatment options may include a combination of chemotherapy and radiation."

McCain's latest diagnosis is not his first battle with cancer. He underwent a procedure in 2000 to remove a type of skin cancer called melanoma from the left side of his face.

McCain, 80, also had a melanoma removed from his left arm in 2000 and another removed from his nose in 2002. Both were determined to be the least dangerous types of melanoma.

McCain's office said in a statement that the Arizona Republican remained in good spirits Wednesday and is confident that any treatments will be effective.

"He is in good spirits as he continues to recover at home with his family in Arizona," his office said.

"He is grateful to the doctors and staff at Mayo Clinic for their outstanding care, and is confident that any future treatment will be effective."

His office said further consultations with his doctors will determine when he will return to the Senate.

Sen. Lindsey Graham (R-S.C.), a close friend of McCain's and one of his most ardent allies on Capitol Hill, spoke with the Arizona senator on Wednesday. He said they talked only briefly about McCain's diagnosis before shifting to a conversation about the Senate's healthcare reform efforts and the National Defense Authorization Act, the federal defense spending bill.

"Literally, it went five minutes until we turned away from what I think most people have a hard time absorbing and focused on what he loves the best," Graham told reporters after speaking with McCain.

The news of McCain's diagnosis prompted an immediate outpouring of support from fellow lawmakers.

"God knows how this ends, not me," Graham said. "But what I do know is this disease has never had a more worthy opponent."

Senate Majority Leader Mitch McConnell (R-Ky.) characterized McCain as a fighter, saying in a statement that "he will face this challenge with the same extraordinary courage that has characterized his life."

"John McCain is a hero to our Conference and a hero to our country. He has never shied away from a fight and I know he will face this challenge with the same extraordinary courage that has characterized his life," McConnell said in a statement. "The entire Senate family's prayers are with John, Cindy and his family, his staff, and the people of Arizona he represents so well."

Sen. John Cornyn (Texas), the No. 2 Senate Republican, echoed McConnell's characterization of McCain and said the diagnosis was "just the latest challenge" for Arizona Republican.

McCain's eldest daughter, Meghan, a Fox News host, said in a statement that her father appeared to be the calmest family member upon receiving the diagnosis.

"It won't surprise you to learn that in all of this, the one of us who is the most confident and calm is my father," she said. "He is the toughest person I know."

President Trump issued a statement shortly after news of McCain's diagnosis broke, calling him a fighter and sending his family well wishes from the White House.

"Senator John McCain has always been a fighter," Trump said. "[First lady] Melania and I send our thoughts and prayers to Senator McCain, Cindy, and their entire family. Get well soon."

Former President Barack Obama, whom McCain ran against in the 2008 presidential election, called his former opponent "one of the bravest fighters" he has ever known, saying that "cancer doesn't know what it's up against."

McCain was first elected to the House in 1982 and won a bid for the Senate just four years later.

Before entering Congress, McCain served in the U.S. Navy as a pilot. While fighting in the Vietnam War, he spent 5 1/2 years as a prisoner of war in North Vietnam.