Arizona Sen. John McCain is returning to the Senate on Tuesday to vote on GOP health care legislation just days after being diagnosed with a brain tumor.

McCain's office made the dramatic announcement late Monday in a brief statement saying he looks forward "to continue working on important legislation including health care reform."

Republicans are holding the high-stakes vote on Tuesday to open debate on legislation to repeal and replace "Obamacare."

They have almost no margin for error making the presence of the 80-year-old McCain crucial if the vote is to succeed.