Scientists say stem cells from a baby's umbilical cord can be stored frozen for at least 15 years.

It offers potential for treating cancer or certain other diseases a child might develop in future life.

However, many doctors urge caution before opting for cord blood storage - as pre-cancerous cells may be present there even at birth.

Cord blood can be cryopreserved for at least 15 years Hal Broxmeyer, Indiana University

The umbilical cords of babies are a rich source of stem cells, the "master cells" of the body.

More than 100,000 samples of frozen cord blood are stored in tissue banks around the world.

It has not been clear, however, for how long they can be successfully stored.

The longest they have been kept before being used for human transplant operations is five years.

However, experiments on rodents suggest the stem cells could last much longer - for up to 15 years.

Human transplants

Scientists in the United States say mouse stem cells survived thawing and were able to grow and divide after 15 years in storage.

The research is published in the online edition of the Proceedings of the National Academy of Sciences.

A team led by Hal Broxmeyer, of the Indiana University of Medicine in Indianapolis, said: "Our results demonstrate that cord blood haematopoietic stem and progenitor cells can be cryopreserved for at least 15 years, and efficiently retrieved in functionally competent form."

They add that human studies must be carried out before there is final proof of the finding.