When Jimmy Carter announced his cancer diagnosis in August, the public’s predictive prognoses were grim.

The former U.S. president, who turned 91 on Oct. 1, was diagnosed with stage IV metastatic melanoma after scans revealed cancerous spots on his liver and four tumors on his brain. His elderly status paired with an extensive family history of fatal cancer (his father, brother, and two sisters all succumbed to the disease) left many wondering how much longer Carter would survive such a medical setback.

In a shocking but incredible turn of events, Carter declared Monday he is now cancer-free.

How?

Carter conquered cancer with a cocktail of radiation and a promising new immunotherapy drug— Merck’s Keytruda.

“Keytruda—known generically as pembrolizumab—targets the activity of genes called PD-1 and PD-L1. The interaction between the two genes lets some tumors escape detection and destruction by immune system cells,” according to NBC News. “PD-1 stops immune cells from attacking normal healthy cells by mistake. Tumor cells make PD-L1 turn on PD-1 when immune cells approach.”

“Keytruda, an engineered immune protein called a monoclonal antibody, disrupts this cloaking effect and lets the immune cells do their job and eat the tumor cell.”

One-year-old Layla Richards from London also received a clean bill of health after suffering from acute lymphoblastic leukemia since she was just three months old. Like Carter, it was an unconventional form of immunotherapy—in this case, gene editing—that gave her a second chance.

“In a last ditch attempt to save the girl’s life, a team at London’s Great Ormond Street Hospital performed an experimental procedure, known as gene editing, previously tested only on mice. First, new genes engineered to attack leukemia cells were injected into immune system cells, called T cells, from a healthy donor. Then doctors used enzymes that act as molecular ‘scissors’ to render those genes impervious to leukemia drugs and prevent them from attacking healthy cells.” The Week

Dr. Paul Veys from Great Ormond Street recently told the BBC, “We’re in a wonderful place compared to where we were five months ago, but that doesn’t mean cure.”

“The only way we will find out if this is a cure is by waiting that one or two years,” he said, “but even having got this far from where we were is a major, major step.”