Sen. John McCain, under treatment for cancer, suffers Achilles' tendon tear in right leg

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WASHINGTON - Sen. John McCain, R-Ariz., who is undergoing treatment for brain cancer, sustained a leg injury that will require him to wear a walking boot until he recovers, his office said Monday.

"Senator McCain was treated at Walter Reed Medical Center over the weekend for a minor tear in his right Achilles' tendon, as well as for other normal and non-life-threatening side effects of cancer therapy," McCain's office said in a written statement.

His office did not specify what the other side effects were. McCain, 81, has "returned to work in the Senate and will be wearing a walking boot until his injured tendon is fully healed," his office said.

McCain was diagnosed this past summer with glioblastoma, a serious form of brain cancer. He announced in September that he was receiving treatment in the Washington-area while he continued working in the Senate.

The longtime lawmaker and current chairman of the Senate Armed Services Committee was a pivotal swing vote during the failed Republican effort to repeal and replace the Affordable Care Act, coming out against two efforts to accomplish that.

He could once again be a key swing vote in the party's biggest current legislative priority: tax reform.