Lewis said he is “clear-eyed” about the prognosis but that his doctors believe recent medical advances have made this type of late-stage cancer treatable. Lewis said has “a fighting chance” and will return to Congress in the coming days to get back to work — though the Georgia Democrat said he might miss a few votes.

Speaker Nancy Pelosi, a longtime colleague and friend, praised Lewis on Twitter, as did dozens of his congressional colleagues on both sides of the aisle. Lewis is seen by many as the "soul" of the House Democratic Caucus, a figure of unquestionable integrity and courage.

"John, know that generations of Americans have you in their thoughts and prayers as you face this fight," Pelosi said. "We are all praying you are comfortable. We know that you will be well."

.@RepJohnLewis, we are all praying for you following this diagnosis. John, know that generations of Americans have you in their thoughts & prayers as you face this fight. We are all praying that you are comfortable. We know that you will be well. pic.twitter.com/j7YMUGLPC2 — Nancy Pelosi (@SpeakerPelosi) December 29, 2019

Lewis, 79, has represented Georgia's 5th Congressional District since January 1987. Lewis defeated fellow civil rights icon Julian Bond the previous September, a stunning political upset that propelled Lewis from the Atlanta City Council to Congress. Both Lewis and Bond subscribed to the Rev. Martin Luther King Jr.’s nonviolent resistance to segregation and had become legends inside the movement. Their struggles over the race turned once close friends into enemies.

Lewis was born in Troy, Ala., a small town south of Montgomery. His parents were sharecroppers, and Lewis was forced to attend segregated schools as a child. The Montgomery bus boycott in the mid-1950s was seminal moment for Lewis, and he was further inspired by King's radio broadcasts.

A student activist who was one of the founders of the Student Nonviolent Coordinating Committee, Lewis was part of the Freedom Rides in 1961, the March on Washington in 1963 and the Bloody Sunday March in 1965, where he was clubbed by a state trooper in Selma, Ala. Lewis was arrested dozens of times during these protests, as well as being attacked by angry mobs.

In 1977, then-President Jimmy Carter appointed Lewis to head up ACTION, a federal volunteer agency. In 1981, Lewis won election to the Atlanta City Council, where pushed ethics reform as a key issue.

Lewis' public stature has grown during his decades of service in Congress. President Barack Obama awarded him the Medal of Freedom in 2011.

"If there’s one thing I love about @RepJohnLewis, it’s his incomparable will to fight. I know he’s got a lot more of that left in him," Obama tweeted. "Praying for you, my friend."

If there’s one thing I love about @RepJohnLewis, it’s his incomparable will to fight. I know he’s got a lot more of that left in him. Praying for you, my friend. — Barack Obama (@BarackObama) December 30, 2019

“With God’s grace, I will be back on the front lines soon,” Lewis said Sunday. “Please keep me in your prayers as I begin this journey.”

Lewis serves on the House Ways and Means Committee, leading the Oversight Subcommittee. Ways and Means Chairman Richard Neal (D-Mass.) said in a Sunday statement his “heart breaks” at the diagnosis and that Lewis has been “a guiding light” on the committee, on Capitol Hill and for the nation.

“I have no doubt that John will fight this terrible disease with the tenacity that’s characterized his lifelong service and pursuit of justice,” Neal said.