Former US president Jimmy Carter said Wednesday that recent liver surgery has shown he has cancer, and that it has spread.
The 39th president, now aged 90, underwent an initially successful operation earlier this month to remove a "small mass."
"That procedure revealed that I have cancer that now is in other parts of my body," he said in a brief written statement.
"I will be rearranging my schedule as necessary so I can undergo treatment."
"A more complete public statement will be made when facts are known, possibly next week," said the Nobel Peace Prize winner, whose two sisters, brother and father all died from pancreatic cancer.
The Georgia native will be treated at Emory University Hospital in Atlanta.
President Barack Obama was among those who voiced their support, wishing his predecessor a "fast and full recovery."
"Jimmy, you're as resilient as they come, and along with the rest of America, we are rooting for you," he said in a statement.
Democratic presidential hopeful Hillary Clinton tweeted : "My thoughts and prayers are with President Carter and his family."
And Vice President Joe Biden spoke with Carter by phone.
"A great man, always upbeat and optimistic. We're praying for him," Biden said.
In May, Carter cut short a trip to Guyana after he took ill.
He was flown back to Atlanta, where attended a public event the next day.
Carter was in the White House from 1977 to 1981.
His term in office is perhaps best known for the Iran hostage crisis, which saw more 52 Americans held in Tehran for 444 days following the Islamic Revolution.
Carter's failure to secure their release, compounded by a failed military rescue attempt, would dog his presidency and scuttle his bid for a second term.
The hostages were only released once Ronald Reagan came to office.
But Carter's reputation is much stronger today than it was when he left office.
Reaching a peace deal between Israel and Egypt is now recognized as the zenith of his presidency and a major diplomatic achievement.
But his work after leaving the White House has also been widely praised.
He has been an extremely active as an ex-president, working as an elections monitor and lobbying for health campaigns via the Carter Center, which he founded in 1982.
He has participated in election monitoring in Mexico, Peru, Nicaragua, Venezuela, and East Timor, and in 2003 traveled to Cuba for a historic face-to-face meeting with longtime communist leader Fidel Castro.
He was recipient of the 2002 Nobel Peace Prize for his tireless efforts to promote social and economic justice.
News of his illness prompted a groundswell of support from well-wishers.
"We hope for his full recovery and return to his inspiring work," said Apple CEO Tim Cook.
"Dems across the country are pulling for you," said Democratic National Committee chair Debbie Wasserman Schultz.
There are four living former US presidents: Carter, George H. W. Bush, Bill Clinton and George W. Bush.