LONDON (Reuters) - A baby boy was born after being conceived with sperm frozen 21 years earlier in what scientists said Tuesday was a new record.

The case will give hope to young men about to undergo treatment for cancer that may leave them infertile.

The boy's father had his sperm frozen when he was 17 before starting successful treatment for testicular cancer in the early 1980s.

"I'm 99% sure that it is the oldest frozen sperm sample used [for a live birth]," said Greg Horne, a senior embryologist at St Mary's Hospital in Manchester, England, which treated the baby's parents.

The man's sperm was stored in liquid nitrogen nearly 2 decades ago and was not thawed until he married and decided to start a family.

Scientists injected a single sperm into the mother's eggs in a technique called intracytoplasmic sperm injection (ICSI) to create embryos. The boy was born 2 years ago after four attempts at in vitro fertilization.

"Even after 21 years of storage, the percentage of motile sperm after thawing was high," said Horne, who reported the case in the journal Human Reproduction.

The man and his wife, who chose to remain anonymous, wanted their case publicized to encourage young cancer patients to have hope for the future.

Young men diagnosed with cancer may become infertile following treatment but they can store sperm beforehand. In Britain sperm can be stored until the man reaches 55.

"This case provides evidence that long-term freezing can successfully preserve sperm quality and fertility. This is important to know because semen stored by young cancer patients is undertaken at a time of great emotional stress when future fertility is unlikely to be an immediate priority," Horne added.

Horne said advancements in fertility treatments, particularly ICSI, have improved the chances of former cancer patients becoming fathers.

Although there have been suggestions that freezing and thawing can damage DNA in sperm, he said there was no evidence that damage was increased by the length of time the sperm was stored.

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