A 9-year-old boy from Los Angeles has made medical history by becoming the youngest stem cell donor at Cedars-Sinai Medical Center. Stephen Mondek volunteered to help save his father’s life through a stem cell transplant to treat the man’s deadly blood cancer.
Dr. Nick Mondek, an anesthesiologist working in the Los Angeles area, was first diagnosed with acute myeloid leukemia in 2022. He received a successful stem cell transplant from his younger brother, which put his cancer into remission. However, earlier this year, the cancer returned and he needed another transplant.
According to The Hill, when Dr. Mondek asked Stephen if he wanted to get tested as a potential donor, the boy’s response was simple and immediate. “The conversation with Stephen was pretty simple,” Dr. Mondek said. “I said, ‘Hey, Buddy, Dad’s sick and they need someone to give me stem cells, and they want to know if you want to get tested to see if you can do it.’” Stephen didn’t hesitate and asked, “When do we go?”
Medical team sees potential in young donor
Dr. Ronald Paquette, clinical director of the Stem Cell and Bone Marrow Transplant Program at Cedars-Sinai Cancer, explained that a half-match donor like Stephen might actually be more effective than a perfect genetic match. Because Stephen shares half his DNA with his father, his immune system could potentially recognize and kill cancer cells more effectively in his father’s bone marrow. The medical team also noted that medical breakthroughs like this often come from unexpected sources.
After testing showed Stephen was a compatible donor, he underwent the donation procedure in July 2025. The high-risk procedure required Stephen to spend several hours in the pediatric intensive care unit with a catheter inserted into a vein in his neck. His stem cells were separated from his blood and frozen.
A week later, Dr. Mondek was admitted to the hospital for six days of chemotherapy to suppress his immune system so it wouldn’t reject Stephen’s donor cells. The transplant then took place, giving Dr. Mondek what doctors call a “stem cell birthday” with a completely new immune system.
Dr. Mondek was discharged from the hospital on August 16, 2025, and made it home in time for the final inning of Stephen’s Little League game. While the transplant shows promise, it will take a year or more to determine if the new immune system can beat the leukemia. Stephen, who turned 10 in August, expressed no regrets about his decision. “I felt good helping my dad,” he said, “and it felt good to have him home.” This remarkable case highlights how health breakthroughs often emerge from family bonds and medical innovation working together.