Former U.S. President and Nobel Peace Prize winner Jimmy Carter announced Sunday that he no longer needs to undergo any more cancer treatments.

Carter was previously diagnosed with melanoma - the deadliest form of skin cancer - which spread to his brain and liver. He will continue to be monitored by a team of doctors.

Carter received radiation and immunotherapy treatment at Emory University's Winship Cancer Institute from last August to February. He also underwent surgery to remove a part of his liver that was affected by tumor lesions. By December, Carter revealed that he was cancer-free, but was still undergoing treatment.

The 91-year-old credited immunotherapy as a vital part of his treatment plan during his announcement at Maranatha Baptist Church in Georgia where he teaches a Sunday class.

"It's a treatment called immunotherapy and it removed the obstacles to my own immune system to fight against cancer, basically - it's kind of complicated," Carter said. "But it's worked very well for me and I had an MRI for 2 hours and 10 minutes and then the doctors determined that I didn't need any more treatment."

Carter received doses of a promising new drug called Keytruda (Pembrolizumab), which was approved shortly before his cancer diagnosis. The drug works by getting the body to actively seek out and attack cancer cells.

Dr. Len Lichtenfeld, the deputy chief medical officer for the American Cancer Society, noted that although Keytruda appeared to be very effective for Carter, doctors still do not know too much about the treatment since it is still very new. Lichtenfled was not involved with Carter's treatment.

"Some people believe they should be continued as long as a patient is doing well, some feel the drugs should continue for a period of time and then be stopped," Lichtenfeld said. "This is clearly a [decision] based on individual evidence specific to the president and made with his doctors."

If the cancer returns, Carter will resume his treatment at the institute, said Deanna Congileo, the spokeswoman for the Carter Center, a nonprofit public policy center. Congileo added that Carter would continue to receive scans to monitor his health.

Despite battling cancer, Carter remained very active throughout his treatment. He had continued to participate in charity, which included working with Habitat for Humanity and the Carter Center.