Former U.S. President Jimmy Carter gestures as he answers questions during "A Conversation with the Carters," as wife Rosalynn Carter looks on during the annual public event at The Carter Center in Atlanta on Sept. 15, 2015. (Tami Chappell/Reuters)

— Former president Jimmy Carter said Tuesday night that he has undergone his second of four treatments for cancer without any “ill effects.”

“We’ll know what the positive effects are later on,” he told an audience here.

Less than a month after Carter announced that cancer had spread to his brain, he and his wife, Rosalynn, addressed more than 400 people at an annual event at the Carter Center.

Carter had a small cancerous mass removed from his liver on Aug. 12, and shortly afterward doctors found four spots of melanoma on his brain. He is being treated with a new immune-boosting drug.

Carter talked about his illness only briefly, saying that the most challenging part of his treatment has been the 64 ounces of liquid that doctors have directed him to drink each day, down from 84 ounces.

“Instead of getting productive work done, I spend a lot of time in the restroom,” he said.

For most of the hour-long discussion, Carter spoke about the center that he and his wife started more than 30 years ago to promote peace and public health abroad.

He said the Carter Center this year monitored its 100th foreign election, in Guyana, and that after nearly three decades of work, the worldwide eradication of guinea worm disease is close.

There are 11 known cases left, down from an estimated 3.5 million in 21 countries, he said: “I hope I’m living longer than that last guinea worm.”

Carter answered questions about foreign policy, ranging from how to manage the European migrant crisis and how to respond to ISIS. The couple also spoke about growing up playing basketball in Plains, Ga., and about their growing family, with 12 grandchildren and 10 great-grandchildren “I can’t keep up,” Rosalynn Carter said.

When asked about their proudest accomplishments, Rosalynn Carter said she is proud of her work on mental health issues, a campaign to reduce stigma and improve services that she began four decades ago.

“So much has changed, and I was there to experience it,” she said.

President Carter cited his time in the White House promoting human rights abroad and protecting the nation’s interests.

“I’m proud I was able to lead this country in a peaceful way,” he said.