AlQa'dah 05, 1436, August 20, 2015, SPA -- Former US president Jimmy Carter is beginning treatments for cancer immediately, he said Thursday, according to dpa. The 90-year-old, who was president from 1977-81, said that a tumour on his liver proved to be melanoma, which is typically a skin cancer. Suspecting the cancer on his liver had spread from elsewhere, doctors eventually found four "very small" melanomas on his brain, which Carter said were "about 2 millimetres." The Nobel peace laureate was due to have received the first in a series of radiation treatments later Thursday for the brain tumours. "I'll do what the doctors recommend for me to extend my life as much as possible," he said in a press conference at his Atlanta-based Carter Centre, a non-profit organization promoting peace and democracy. "So I don't look on this as any hardship on me. They have means, they say - and I trust them completely - to alleviate the after-effects or side effects of different treatments. ... I don't anticipate any troubling pain or suffering or deprivation on my part." US President Barack Obama, a fellow left-leaning Democrat, tweeted encouragement Thursday for his predecessor: "We're all pulling for you, Jimmy." Wearing a dark blue jacket, red tie and blue jeans, Carter was steady as he walked alone into a conference room and sat at a table with a microphone. Typically a soft-spoken orator, he spoke in restrained but clear and steady voice. The liver tumour, which he said was 2.5 cubic centimetres, was removed in an operation on August 3. Carter announced August 12 that he had cancer. After the surgery, believing the tumour was completely removed, he was "quite relieved." Within hours, though, the brain lesions turned up in a scan prompted by the biopsy finding of melanoma. "That night and the next day until I came back up to Emory (hospital), I just thought I had a few weeks left," Carter said. "But I was, surprisingly, at ease. You know, I've had a wonderful life, I had thousands of friends, and I've had an exciting and adventurous, gratifying existence." He is now more hopeful and has not ruled out a planned annual house-building mission slated for November in earthquake-shattered Nepal. But Carter gave no specific long-term prognosis. "Now I feel, you know, it's in the hands of God, whom I worship," he said, "and I'll be prepared for anything that comes." Throughout his globe-trotting career, Carter has famously remained active in the Baptist church in his hometown of Plains, Georgia, population 700, about 250 kilometres south of Atlanta. "I plan to teach Sunday school this Sunday and every Sunday, as long as I'm physically and mentally able, in my little church," he said. "And we have hundreds of visitors who come to see the curiosity of a politician teaching the Bible." Carter had suffered a "very bad cold" in May in South America, while on an election monitoring mission in Guyana, and returned to Atlanta for a medical exam at Emory University, which has a leading medical centre. A physical and MRI found a likely cancerous growth on his liver, Carter said. He only informed his wife of 69 years, former first lady Rosalynn, about it on June 15. "We knew, I would say, the end of June that I had to have an operation on my liver," Carter said. "But I had an extensive book tour scheduled ... and I wanted to do that, and the doctors told me that it was a very slow-growing cancer apparently. It wouldn't make any difference between the middle of July and August 3." "They had a very high suspicion then and now that the melanoma started somewhere else on my body and spread to the liver," Carter said. "The doctors tell me that about 98 per cent of all the melanoma is skin cancer and about 2 per cent of the melanomas are internal."