Jimmy Carter

ATLANTA — A recent MRI showing no cancer on Jimmy Carter’s brain is “very positive” news for the former president but will not end his medical treatment, doctors said.

Carter, 91, announced Sunday doctors found no evidence of the four lesions discovered on his brain this summer and no signs of new cancer growth. He revealed in August he had been diagnosed with melanoma and had begun treatment, including surgery to remove part of his liver, targeted radiation therapy and doses of a recently approved drug to help his immune system seek out any new cancer cells.

Carter said he will continue every three weeks to receive the drug, Keytruda, one type of “immunotherapy” that melanoma specialists credit for improving treatment of the disease without the side effects of traditional chemotherapy drugs that can cause hair loss and other symptoms, said Dr. Douglas Johnson, a melanoma specialist at Vanderbilt-Ingram Cancer Center who is not involved with Carter’s treatment.

The drugs also have shown promise as a “long-lasting” treatment, but doctors continue to learn more as the drugs are used outside of clinical trials, he said.

Carter has said he experienced no side effects during treatment, a positive sign for his doctors, said Dr. Keith Flaherty, a melanoma specialist at Massachusetts General Hospital’s Termeer Center for Targeted Therapies who is not involved in Carter’s treatment.

“If (a patient) breaks the right way, the likelihood that he will do well in the short term is extremely high,” Flaherty said.