Good wishes poured in on social media after Carter's announcement, while President Barack Obama said he and first lady Michelle Obama wish Carter 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," Obama said in a statement.

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, said Lichtenfeld. 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.