Infertile women have been offered new hope after scientists found that a common cancer drug triggers the development of new eggs, an outcome previously thought to be impossible.
In a discovery hailed as "astonishing", researchers at the University of Edinburgh proved that it is possible to reverse the clock and coax the ovaries back into a pre-pubescent state where they begin to produce new eggs.
Women are born with all their eggs, which is why conceiving grows harder with age, as the eggs become old and damaged before running out entirely.
But scientists noticed that women who had undergone chemotherapy for Hodgkin Lymphoma with a drug combination known as ABVD had up to 10 times the number of eggs as healthy women. Far from damaging the chance of having a baby, the cancer drugs may actually have improved their fertility.
The researchers speculate that the shock of chemotherapy may trigger stem cells in the ovaries into producing new follicles, the hair-like structures that each produce a single egg.
Lead researcher Professor Evelyn Telfer, of the University of Edinburgh's school of biological sciences, said: "We were astonished when we saw what had happened to the tissue. It looked like pre-pubescent tissue with a high density of follicles and clustering that you don't normally see in an adult.
"We knew that ABVD does not have a sterilising effect like some cancer drugs can, but to find new eggs being made, in such huge numbers - that was very surprising to see."
Professor Telfer said the outcome of the study may prove to be "significant and far-reaching", adding that "it is significant that the same effect was seen in all of the women on ABVD".
Scientists analysed samples of ovarian tissue donated by 14 women who had undergone chemotherapy, alongside tissue from 12 healthy women.
They found that the tissue from eight of the cancer patients treated with ABVD had between four and 10 times more eggs compared with tissue from women who had received a different chemotherapy, or healthy women of a similar age. The ovarian tissue was in healthy condition, appearing similar to tissue from young women's ovaries.
Although the eggs are in an immature state, the scientists are trying to discover how they were created, then work out a way to bring them to maturity. It is unclear if the eggs in their current form would be functional.
Professor Charles Kingsland, a fertility expert at Liverpool Women's Hospital, said: "This is a very small but extremely interesting study. It's very early days but may give an insight as to how the ovary can make new eggs, which previously we thought was impossible."
The study was published in the journal Human Reproduction.
The Telegraph, London