ATLANTA — With a broad smile and an upbeat attitude, former President Jimmy Carter told the world Thursday that he has cancer in his brain, and feels “perfectly at ease with whatever comes.”

Carter said doctors had removed melanoma from his liver, but found four small tumors in his brain. Later Thursday, he received radiation treatment. He also began receiving injections of a newly approved drug to help his immune system seek out and destroy the cancer cells wherever else they may appear.

Wearing blue jeans and a blazer, Carter spoke with good humor and unsparing honesty, revealing that he had kept suspicions of cancer from his wife, Rosalynn, for weeks until the diagnosis was confirmed in June.

“Now I feel it’s in the hands of God, whom I worship, and I’ll be prepared for anything that comes,” he said.

Carter’s team of doctors at Emory Health Care includes Dr. Walter Curran Jr., who runs Emory’s Winship Cancer Institute. Treatments for melanoma have improved tremendously recently, and Carter’s prospects are good even at the age of 90, Curran said. But he cautioned against the idea that Carter can be “cured.”

“We’re not looking for a cure in patients who have a disease like melanoma that has spread,” Curran said. “The goal is control and to have a good quality of life.”

Carter said he thought the cancer was only in his liver and was removed with surgery on Aug. 3, but an MRI exam that same afternoon showed the spots on his brain. Carter said he went home that night thinking he had only a few weeks to live, but found himself feeling “surprisingly at ease.”

The former president didn’t discuss his long-term prognosis, but said he will cut back dramatically on his humanitarian work while following the orders of a team that includes the world’s best “cancer-treaters.”

His treatment regimen will include four injections of pembrolizumab, which was approved by the FDA for melanoma patients last year, at three-week intervals.

“This is not a eulogy in any way,” said grandson Jason Carter, who is taking over as chairman of the board of trustees at the Carter Center, which promotes peace, democracy and health care improvements around the world.

Still, his grandfather’s responses to reporters often expanded into reflections on his life, faith and family.

“I’ve had a wonderful life,” Carter said. “I’ve had thousands of friends, I’ve had an exciting, adventurous and gratifying existence. So I was surprisingly at ease, much more so than my wife was.”