Former US President Jimmy Carter delivered an unexpected message on Sunday to the several hundred people gathered at a Baptist church in Georgia for his Bible lesson - his latest brain scan showed no sign of cancer.

Carter, 91, started treatment in August for melanoma that had spread from his liver to his brain. A previous MRI test showed the four spots of cancer that had developed on his brain were responding to treatment, he said.

‘When I went this week, they didn’t find any cancer at all, so I have good news,’ Carter told the crowd at Maranatha Baptist Church in his hometown of Plains, Georgia, according to a video from NBC News.

The former Democratic president, known for his unassuming style, offered a quick smile as people who had come for the Sunday School class he teaches gasped and clapped.

In a brief written statement afterward, Carter confirmed his most recent brain scan ‘did not reveal any signs of the original cancer spots nor any new ones.’

He said he would continue to receive regular doses of pembrolizumab, a new treatment that is part of a promising class of drugs that harness the body’s immune system to fight cancer. The immunotherapy is manufactured by Merck & Co under the brand name Keytruda.

While about 30 per cent of patients treated with the drug experience significant shrinkage of their cancer, only approximately 5 percent experience complete remission, said Dr. Marc Ernstoff, director of the melanoma program at the Cleveland Clinic’s Taussig Cancer Institute in Ohio.

On average, the immunotherapy treatment extends a recipient’s life expectancy by a year and a half.

‘But people that are in complete remission tend to live significantly longer,’ said Ernstoff, who is not involved in Carter’s care.

Carter, who said after his diagnosis last summer that his fate was ‘in the hands of God,’ has defied expectations before.

Critics derided his 1977-1981 presidency as a failure, although he played a key role in negotiation of the 1978 Camp David peace accord between Israel and Egypt. He lost his 1980 re-election bid to Republican Ronald Reagan.

But the former peanut farmer built one of the most successful post-White House legacies, winning a Nobel Peace Prize in 2002 and remaining active into his ‘90s in causes such as fighting disease in Africa and building homes for the poor.

He said in August that his cancer treatment, which has included radiation, would require him to cut back dramatically on his public schedule.

But Carter has continued to teach Sunday School classes and participated in at least one Habitat for Humanity home-building event this autumn. In October, he announced he was also working with the Rev. Martin Luther King Jr.’s heirs to help mediate their dispute over whether to sell their father’s 1964 Nobel Peace Prize medal and the Bible he carried during the civil rights movement.