A medical team in Israel has given Girls as young as 5 who suffer from cancer a chance to preserve their fertility after chemotherapy.
Doctors have extracted, matured and frozen eggs from girls that will allow them to become parents when they grow up.
Childhood cancers usually result in cure rates of between 70 and 90 percent but the aggressive chemotherapy which is often needed can render children sterile. The life saving chemotherapy and radiotherapy can cause infertility by destroying the ovaries containing the lifetime stock of eggs or shorten a woman's fertile period.
For the first time Israeli doctors have found eggs in ovarian tissue taken from girls as young as five - and say they will offer the treatment to girls aged three.
They have frozen 167 eggs from 17 girls aged five to 20, in addition to ovarian tissue containing egg producing follicles. The eggs were then cultured to make them viable.
In the case of the five-year-old, who is still receiving therapy for kidney cancer, seven eggs were obtained, one of which was successfully matured.
Ariel Revel from Hadassah University Hospital in Jerusalem will present full details of his research at the annual meeting of the European Society of Human Reproduction and Embryology in Lyon, France, this week.
"We were able to extract oocytes \ using needle aspiration from very young girls," he told the European Society of Human Fertilization and Embryology conference in Lyon.
Scientists believe the frozen eggs stand a good chance of producing a pregnancy after being artificially fertilised.
While eggs, ovarian tissue and fertilized embryos can be harvested from female patients who are sexually mature, there have been few options available to children. Many experts had thought eggs in the follicles of young girls before puberty were too immature to be extracted.
The same technique could also be employed on older women with cancer, some of whom cannot be given hormonal drugs to stimulate the ovaries before egg collection.
Dr Ariel Revel, who led the team, said: "No eggs have yet been thawed, so we do not know whether pregnancies will result. But we are encouraged by our results so far."
A spokesperson for the Teenage Cancer Trust said: "This offers hope to many young female cancer survivors that they may have a chance in the future of re-establishing their fertility."
Gillian Lockwood, head of Midland Fertility Services, the only clinic in Britain to have live births from frozen eggs, said: "If it works its good news, because the big block has always been that we thought you had to wait until they reached puberty before getting the eggs. But this raises significant ethical issues. The parents will be making the decision in these cases, and it may be that they are keen to have grandchildren, and I don't know if a very young girl will fully appreciate all of the arguments."