More and more people are surviving childhood cancer, but nearly one in three will be left infertile from the chemotherapy or radiation that helped save their lives.

When young adults are diagnosed with cancer, they can freeze sperm, eggs or embryos ahead of treatment. But children diagnosed before puberty can't do that because they're not yet producing mature eggs or sperm.

"Fertility issues for kids with cancer were ignored" for years, said University of Pittsburgh reproductive scientist Kyle Orwig. "Many of us dream of growing up and having our own families. We hope our research will help these young patients to do that."

Orwig's team reported a key advance on Thursday: First, they froze a bit of testicular tissue from a monkey that hadn't yet reached puberty. Later, they used it to produce sperm that, through a monkey version of IVF, led to the birth of a healthy female monkey named Grady.

The technique worked well enough that human testing should begin in the next few years, Orwig said.

"It's a huge step forward" that should give hope to families, said Susan Taymans of the National Institute of Child Health and Human Development, which helped fund the research published in the journal Science. "It's not like science fiction. It's something that seems pretty attainable."

University of Pittsburgh Medical Centre and a handful of other hospitals already freeze immature testicular tissue from young cancer patients, in hopes of knowing how to use it once they're grown and ready to have their own children.

Boys are born with stem cells inside little tubes in the testes, cells that start producing sperm after puberty's testosterone jolt. Orwig's goal: Keep sperm-producing stem cells safe from cancer treatment by freezing small pieces of testicular tissue, and using them to restore fertility later in life.

How? Enter the monkey research.

Orwig's team froze tissue from young male monkeys, and then sterilised them. Once the monkeys approached puberty, the researchers thawed those tissue samples and gave them back to the original animal - implanting them just under the skin.

"We're not hooking it up to the normal plumbing," Orwig cautioned.

Boosted by hormones, the little pieces of tissue grew. Months later, the researchers removed them. Sure enough, inside was sperm they could collect and freeze.

Colleagues at the Oregon National Primate Research Centre injected some of that sperm into eggs from female monkeys and implanted the resulting embryos. Last April, Grady was born, and "she plays and behaves just like every other monkey that was grown the normal way," Orwig said.

Orwig is also researching ways to reinsert sperm-producing stem cells where they belong rather than the more roundabout technique.

Australian Associated Press