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. It said further information will be provided when more facts are known, "possibly next week."
Carter, 90, announced on Aug. 3 that he had surgery to remove a small mass from his liver.
Carter was the nation's 39th president, defeating Gerald Ford in 1976 with a pledge to always be honest. A number of foreign policy conflicts doomed his bid for a second term, and Carter lost to Ronald Reagan in a landslide.
After leaving the White House, he founded the center in Atlanta in 1982 to promote health care, democracy and other issues globally often with wife, Rosalynn by his side, and won a Nobel Peace Prize in 2002.
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 also completed a book tour this summer to promote his latest work, "A Full Life."
Carter included his family's history of pancreatic cancer in that memoir, writing that his father, brother and two sisters all died of the disease and said the trend "concerned" the former president's doctors at Emory.
"The National Institutes of Health began to check all members of our family regularly, and my last remaining sibling, Gloria, sixty-four, was diagnosed with pancreatic cancer and died in 1990," Carter wrote. "There was no record of another American family having lost four members to this disease, and since that time I have had regular X-rays, CAT scans, or blood analyses, with hope of early detection if I develop the same symptoms."
Carter wrote that being the only nonsmoker in his family "may have been what led to my longer life."
"Our thoughts and prayers go out to President Carter," said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society.
"There's a lot we don't know," but the first task likely will be determining where the cancer originated, as that can help determine what treatment he may be eligible for, Lichtenfeld said. Sometimes the primary site can't be determined, so genetic analysis of the tumor might be done to see what mutations are driving it and what drugs might target those mutations.
"Given the president's age, any treatments, their potential and their impacts, will undoubtedly be discussed carefully with him and his family," he added.
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.An Emory spokesman declined comment Wednesday. The health care system's Winship Cancer Institute in Atlanta touts its designation as a National Cancer Institute center and a recent U.S. News and World Report ranking among the top 25 cancer programs in the U.S. on its website