More children than ever before are beating cancer, with between 70 and 90 percent of victims surviving until adulthood. However, many of the medical procedures developed to save children's lives result in making the children incapable of reproducing as adults.

Samples of sperm can be taken before cancer treatment starts from boys who have reached puberty and then frozen until they are adults. However, younger children were often left infertile, without a way to ever have children of their own - until now.

Researchers from Yokohama City University in Japan took samples of testis tissue from newborn mice. They then froze the samples, either by a slow cooling process, or by turning it into a glass-like substance. After the tissues were thawed, they were placed on an agarose sugar culture. Soon, the material started producing sperm cells. These were then placed into female mice, which became pregnant, and gave birth to healthy young. This next generation was capable of producing their own children through normal mating.

"We are now working on human samples, which are very different from mice tissue, I have to find some trick to make it work, so it's very difficult to predict how long that will take," Takehiko Ogawa of Yokohama City University said.

Without this process, the only other way of restoring fertility in men who went sterile as boys due to cancer would have been to take samples of testis tissue before treatment, then transplant that material back into the bodies when they were old enough to have children. That procedure would carry the risk of re-introducing the cancer.

This new procedure would "check that lab-made sperm were genetically normal and that any babies born are going to be healthy and fertile themselves... based on this research in mice, the data looks encouraging and I hope that proper trials in humans will soon begin," Allan Pacey, a fertility researcher at the University of Sheffield, told reporters.

Another technological hurdle to be overcome in adapting this technique for human use is the immature nature of the tissue taken from per-pubescent boys. Their cells are not mature enough to produce sperm, so a way to accelerate development of the tissues would need to be developed. It is possible exposure to testosterone could significantly speed the process, allowing the reproductive cells to form. Male mice begin producing sperm early on in their life cycles, while it takes human males a decade or more to begin manufacture of the cells.

Research into how testicle samples can be saved and cultured to produce sperm was detailed in the journal Nature Communications.