Doctors have discovered a new surgical technique that could improve a man’s fertility after surviving cancer as a child.

Many forms of cancer treatments save lives, but can also cause infertility. Those young men diagnosed before puberty often do not have enough time to bank sperm, losing their hope of becoming a father in the future.

Now, hospitals and researchers are paying close attention to find a solution. Long-term data is now available to help find other options for childhood cancer survivors besides adoption or using donor sperm.

Researchers at New York-Presbyterian Hospital and Weill Cornell Medical Center pioneered an option a decade ago for men deemed sterile for a number of reasons.

Surgeons essentially perform tiny biopsies of testicular tissue to hunt any pockets of hidden sperm, which then are used in standard in vitro fertilization to attempt a partner's pregnancy.

In cancer survivors, they were able to extract small amounts of sperm from more than a third of the men — 27 of 73. Doctors then attempted injecting the sperm into a partner's eggs in hopes of pregnancy. The result: 20 children were born, including five pairs of twins, the researchers reported Monday in the Journal of Clinical Oncology.

Being able to find what are essentially stray sperm cells is dramatic but doesn't mean the technique will help everyone, cautions Dr. Peter Schlegel, urology chairman at NY-Presbyterian/Weill Cornell.

"Chances of successful treatment before were thought to be zero. So yes, we're far better than zero but certainly it's not absolute that if you go in for treatment, that you're going to be successful," he said.

The new study found that the best chance for sperm retrieval was among men who'd been treated for testicular cancer, while survivors of sarcoma had the lowest chance. That's because of varying treatments for different types of cancer.

Sperm is made in tiny tubes inside the testicles, which can be seen under an operating-room microscope, Schlegel explained. Flat tubes probably contain no sperm, while larger ones are removed to see if they do.

The surgery costs about $10,000 to $12,000, in addition to the costs of IVF, he said. It's already offered at various medical centers around the country.

"This study gives men a new way to achieve fertility and the potential of parenthood," Dr. Lisa Diller of the American Society of Clinical Oncology said in a statement.

The Associated Press contributed to this report.