Rep. John Lewis, D-Ga., an icon of the civil rights movement, will undergo treatment for stage 4 pancreatic cancer, his office said Sunday.

He learned of the diagnosis this month, after what Lewis, 79, described as a "routine medical visit and subsequent tests."

"While I am clear-eyed about the prognosis, doctors have told me that recent medical advances have made this type of cancer treatable in many cases, that treatment options are no longer as debilitating as they once were, and that I have a fighting chance," Lewis said in the statement.

Lewis, who represents Georgia's 5th Congressional District, covering most of Atlanta, said he plans to return to Washington "in coming days to continue our work and begin my treatment plan, which will occur over the next several weeks."

Lewis, who was elected to Congress in 1986, referred to the various battles he has faced throughout his career.

"I have been in some kind of fight — for freedom, equality, basic human rights — for nearly my entire life. I have never faced a fight quite like the one I have now," he said.

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Lewis received an outpouring of support online from colleagues and two former presidents.

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

"If there's anyone with the strength and courage to fight this, it's you, John," former President Bill Clinton tweeted on Sunday. "Hillary and I love you, and we join with millions of other Americans in praying for you and your family."

"Praying for my friend and hero @repjohnlewis who has as much bravery and strength as anyone I've ever known," Sen. Chris Coons, D-Del., wrote on Twitter.

Rep. Veronica Escobar, D-Texas, tweeted: "I am so deeply saddened by this news. Knowing and working with him has been one of the greatest blessings of my life in public service. But I also have faith that John Lewis will beat this. He is a warrior like no other. Sending you much love and all my prayers, @repjohnlewis."

Nearly 57,000 people in the United States will have been diagnosed with pancreatic cancer in 2019, according to the American Cancer Society. The disease, which accounts for about 7 percent of all cancer deaths, is more common in men than women, it said.