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Former President Jimmy Carter says he has cancer that has spread, although it’s not yet clear what kind of cancer he has.

Carter, 90, had a mass removed from his liver on Aug. 3.

“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 said in a statement.

James Earl Carter Jr. was 39th president of the United States, from 1977 to 1981. He’s kept active despite his age, working with groups such as Habitat for Humanity, winning the Nobel Peace Prize in 2002 and founding the nonprofit Carter Center in his home state of Georgia.

“Recent liver surgery revealed that I have cancer that now is in other parts of my body."

Carter’s family has a history of pancreatic cancer. His father, both his sisters and his brother died of pancreatic cancer, and his mother had pancreatic cancer as well.

In 2007, Carter told The New York Times that he had CT scans twice a year and later MRI (magnetic resonance imaging) to look for tumors in his pancreas.

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In May, Carter left Guyana early from a stint monitoring elections there, saying he was feeling unwell.

Pancreatic cancer can spread to other organs, including the liver, and cancer can also originate in the liver and spread elsewhere. Carter did not give details of what type of cancer he has or how far it has spread.

However, when cancer spreads from one organ to elsewhere in the body, it is considered Stage IV cancer -- the most advanced stage. Stage IV cancer is generally incurable, although it can be treated, depending on the type.

Dr. Robert Mayer, a gastrointestinal cancer specialist at the Dana Farber Cancer Institute, says that at age 90, Jimmy Carter is unlikely to tolerate much treatment.

There are many different possible cancers that Carter could have, Mayer said.

"This is a 90 year old gentlemen with apparent widespread disease. The goals of treatment would be his comfort."

"I really don’t know from paucity of information which of these would be the situation for President Carter. I don’t know what his symptoms were. I don’t know what led to surgery on his liver," Mayer told NBC News.

"This is a 90-year-old gentleman with apparent widespread disease. The goals of treatment would be his comfort. If chemo is considered it would need to take into account his age."

Mayer says a 90-year-old patient cannot tolerate the same treatment that could buy years of life for cancer patients in their 60s or 70s.

Statements of support poured in, including from President Barack Obama.

"Our thoughts and prayers are with Rosalynn and the entire Carter family as they face this challenge with the same grace and determination that they have shown so many times before," Obama's statement read.

"Jimmy, you're as resilient as they come, and along with the rest of America, we are rooting for you."