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Hsu, now 26, is the first to return as an adult and test if reimplanting those cells might work.

“The science behind it is so incredibly new that right now it’s kind of a waiting game,” said Hsu, of Vienna, Virginia. “It’s kind of eagerly crossing our fingers and hoping for the best.”

It may seem unusual to discuss future fertility when a family is reeling from the diagnosis of a child’s cancer. But 85% of children with cancer now survive to adulthood and about 1 in 3 are left infertile from chemotherapy or radiation.

Young adults with cancer can bank sperm, eggs or sometimes embryos ahead of treatment. But children diagnosed before puberty don’t have that option because they’re not yet producing mature sperm or eggs.

Boys are born with stem cells inside spaghetti-like tubes in the testes, cells that start producing sperm after puberty sparks a rise in testosterone. With , Pitt reproductive scientist Kyle Orwig studies how to preserve and potentially use testicular cells to restore fertility.

It starts with a biopsy-like removal of a small amount of testicular tissue that contains millions of cells – some of them precious sperm-producing stem cells. from about 1,000 prepubertal boys.

It’s impossible to tell if enough stem cells are in each tiny sample to matter. But in 2019, Orwig used preserved testicular tissue from a young male monkey that, in an animal version of IVF, led to the birth of a healthy baby monkey.

By 2023, Orwig was ready to reimplant now-grown cancer survivors’ cells when Hsu — not ready to start a family yet but curious about his long-ago study participation — reached out.

“We’re not expecting a miracle result,” cautioned Orwig, whose colleagues transplanted Hsu’s thawed cells in November 2023.

In a paper this week, Orwig reported the injection, guided by ultrasound to the right spot, was safe and easy to perform. His work has not yet been reviewed by other scientists.

And Orwig said it's too soon to know if the experiment worked and standard tests likely won't tell, as animal testing found assisted reproduction techniques were needed to detect and retrieve small amounts of sperm. Still, he hopes the ongoing research will alert more families to consider fertility preservation so they'd have the option if it eventually pans out.

Belgian researchers announced a similar experiment in January, implanting pieces of testicular tissue rather than cells in a childhood cancer survivor.

“These developments are of great importance,” said researcher Ellen Goossens of Vrije Universiteit Brussel. While animal research “was very promising, transplantations in humans will be the only way” to tell if this really works.

Similar research with immature ovarian tissue is underway for female childhood cancer survivors, too, noted Dr. Mahmoud Salama, who directs the Oncofertility Consortium at Michigan State University.

Hsu said even if his experimental transplant doesn’t work, it will guide further research. He’s grateful his parents years ago “made a call that gave me the option to make the choice for myself today.”

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.