10-year-old becomes youngest-ever stem cell donor – saving his father’s life

When Los Angeles anesthesiologist Dr. Nick Mondek learned his leukemia had returned earlier this year, he feared his options were running out. A stem cell transplant from his brother had given him remission once before, but now the cancer was back. No other relatives or registry matches could be found.

Then came a bold idea: Could his 9-year-old son Stephen step in?

Mondek knew it was a long shot. Donors are rarely that young, and the procedure would mean weeks of preparation and a day in intensive care. But when he posed the question to his son, the answer came without hesitation.

“When do we go?” Stephen asked.

Acute myeloid leukemia, or AML, is an aggressive cancer of the blood and bone marrow. It requires fast treatment because the disease can worsen in weeks. Transplants offer the best chance at survival, but finding the right match is notoriously difficult.

Dr. Ronald Paquette, clinical director of the Stem Cell and Bone Marrow Transplant Program at Cedars-Sinai Cancer, knew Mondek needed a new strategy. “We followed every clinical protocol, but the disease still managed to come back,” Paquette said. “How could we treat his cancer a second time and have a better chance it doesn’t return?”

The answer was Stephen. Because children inherit half their DNA from each parent, Stephen was a “half-match.” Doctors explained that sometimes half-matched cells may be even better at recognizing and destroying cancer. Younger donors also tend to give more resilient stem cells.

Dr. Hoyoung Chung, a pediatric critical care doctor at Cedars-Sinai Guerin Children’s, called Stephen’s donation “very rare” and praised the boy’s courage.

Before the procedure, Stephen underwent a full evaluation to confirm he was healthy and understood the process. For weeks, he prepared with medications that boosted his stem cell count. On donation day, he was admitted to the pediatric intensive care unit.

Doctors placed him under general anesthesia and inserted a catheter into a neck vein. Over six hours, his blood cycled through a centrifuge that separated the stem cells. The cells were collected, frozen, and saved for transplant.

For his father, waiting was the hardest part. “I put people to sleep every day, so I reassured myself that everyone wakes up,” Mondek said. “But those 60 minutes when Stephen was asleep were probably the toughest of the whole process.”

By that evening, the family was back home together.

A week later, it was Mondek’s turn. Six days of chemotherapy weakened his immune system so it wouldn’t fight Stephen’s donor cells. Then came transplant day, what doctors call a “stem cell birthday.”

“The patient knows they cannot survive without the stem cells,” Paquette said. “The delivery of the stem cells into their body is like a rebirth.”

Mondek stayed in the hospital for two weeks while Stephen’s cells began building a new immune system inside him. On August 16, he was finally discharged—just in time to watch Stephen play in the last inning of a Little League game.

Stephen, now 10, downplayed his role. “I felt good helping my dad,” he said, “and it felt good to have him home.”

To Mondek, his son’s quiet bravery is nothing short of heroic. “He didn’t have to put on a cape or leap buildings in a single bound,” he said. “Instead, he put on a hospital gown and gave me hope.”

Stephen’s classmates seemed to agree. “It feels good to do that, because all my friends are proud of me,” he told KABC, Los Angeles’ ABC station.

Within days, he was back at baseball practice. His father, meanwhile, continues the slow climb toward recovery. A recent blood test showed no trace of leukemia cells, and Mondek remains in remission. Doctors caution it could take a year or more to know if Stephen’s stem cells have fully beaten the cancer. But optimism runs high.

Dr. John Chute, director of Hematology and Cellular Therapy at Cedars-Sinai, said Mondek’s case shows the impact of personalized medicine. “Our exceptional patient care is part of the reason that our transplant program has enjoyed consecutive top 10 national rankings by the Center for International Blood and Marrow Transplant Registry since 2021,” Chute said.

For Mondek, this chapter has reshaped how he sees both medicine and parenthood. “Everything lined up for this,” he said. “Dr. Paquette said the perfect donor would be young, healthy, and a 50 percent match, and he was right here in front of us.”

The family knows the road ahead will still include setbacks and uncertainty. Yet Mondek says his son’s willingness to step forward gave him more than just a transplant. It gave him time, hope, and a renewed sense of life.

“Stephen is proof that real-life heroes come in all shapes, sizes, and even ages,” Mondek said. “They may be right in front of us, and in one act of courage, they can completely alter your life.”

According to the American Cancer Society, Acute Myeloid Leukemia begins in the bone marrow, the soft center of certain bones where blood is formed. In most cases, the disease quickly enters the bloodstream. From there, it can spread to the lymph nodes, liver, spleen, brain, spinal cord, or even the testicles. In some patients, the abnormal cells cluster into a mass called a myeloid sarcoma.

This illness often grows out of immature myeloid cells, which normally become white blood cells. It may also affect early forms of red blood cells or the cells that create platelets. Because it advances quickly, treatment usually starts right after diagnosis. Doctors recognize several subtypes, based on how developed the cancerous cells look compared with healthy ones.

To understand the damage, it helps to know how blood is made. Bone marrow contains stem cells, fat, and support tissue. Stem cells can turn into lymphocytes or other myeloid cells. Myeloid cells give rise to red blood cells, which carry oxygen, platelets, which help blood clot, and white blood cells, which fight infections. In this disease, some of those myeloid cells grow abnormally and overwhelm the body’s normal defenses.

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