Sen. John McCain opened up about his battle with brain cancer on Sunday, adding it to the list of other near-fatal encounters he's faced.“I’m facing a challenge," he said on CNN's "State of the Union." "But I’ve faced other challenges, and I’m very confident about getting through this one as well.”In his first nationally televised interview since his diagnosis in July, McCain discussed with CNN's Jake Tapper some of the details of his battle against glioblastoma, an aggressive type of brain cancer.