Sen. John McCain, 80, has been diagnosed with a primary glioblastoma, a type of brain tumor, Mayo Clinic doctors directly involved in the senator's care told CNN exclusively.

Sen. John McCain, 80, has been diagnosed with a primary glioblastoma, a type of brain tumor, Mayo Clinic doctors directly involved in the senator's care told CNN exclusively.

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McCain Faces His Greatest Battle

John McCain has always lived for the fight. Now he's facing his toughest battle.