Sen. John McCain is back in the hospital getting treatment for side effects from his treatment for brain cancer, his office confirmed Wednesday.

“As ever, he remains grateful to his physicians for their excellent care, and his friends and supporters for their encouragement and good wishes. Senator McCain looks forward to returning to work as soon as possible,” his staff said in a statement.

The 81-year-old Arizona Republican revealed last summer that he had been diagnosed with a deadly form of brain cancer known as glioblastoma.

His hospitalization at Walter Reed Medical Center comes as the Senate prepares to vote next week on the GOP tax reform bill.

Republicans hold a razor-thin majority of 52 to 48 seats until Sen.-elect Doug Jones is sworn in — and can’t afford to lose more than two votes from their caucus.

But the Alabama Democrat won’t be sworn in until after the tax reform vote.