Carter, 90, announced the diagnosis in a statement from the Carter Center on Wednesday afternoon.
"Recent liver surgery revealed that I have cancer that now is in other parts of my body. I will be rearranging my schedule as necessary so I can undergo treatment by physicians at Emory Healthcare. A more complete public statement will be made when facts are known, possibly next week."
Carter announced on Aug. 3 that he had surgery to remove a small mass from his liver. The statement makes clear that Carter's cancer is widely spread, but not where it originated, or even if that is known at this point. The liver is often a place where cancer spreads and less commonly is the primary source of it.
Carter's father, two sisters and brother died of pancreatic cancer. His mother also died of cancer.
Thanks to everyone for your thoughts and prayers for my grandfather and grandmother. I will pass them along!— Jason Carter (@SenatorCarter) August 12, 2015
Carter was the nation's 39th president. After leaving the White House, he founded the center in Atlanta in 1982 to promote health care, democracy and other issues globally.
He has remained active for the center in recent years, making public appearances at its headquarters in Atlanta and traveling overseas including a May election observation visit to Guyana cut short when Carter developed a bad cold.
Carter Center spokeswoman Deanna Congileo called the surgery earlier this month "elective" and said Carter's "prognosis is excellent for a full recovery. She declined to answer further questions at the time.
The Associated Press contributed to this report