WASHINGTON -- Arizona Sen. John McCain says he’s grateful for the outpouring of support after his brain cancer diagnosis. He’s promising to be back soon.

In a tweet Thursday, McCain says: “I greatly appreciate the outpouring of support - unfortunately for my sparring partners in Congress, I’ll be back soon, so stand-by!”

McCain’s office said late Wednesday that the 80-year-old senator had been diagnosed with cancer. Doctors in Arizona removed a blood clot above his left eye last Friday. Pathology tests revealed a brain tumor associated with the clot.

McCain’s best friend in the Senate says the brain cancer diagnosis was a shock, but that the 80-year-old lawmaker is focused now on getting better.

South Carolina Sen. Lindsey Graham says “the-woe-is-me thing isn’t part” of McCain’s DNA. But Graham said Thursday he expects McCain to return to the Capitol only when he is “fit to fight.”

McCain has survived several near-death experiences, including being shot down over Vietnam in 1967 and surviving 5½ years as a prisoner of war.

Graham says, “One thing John has never been afraid of is death.”

Graham says he spoke to McCain Wednesday evening. The senator is recuperating at his home in Arizona.