Science has long taught us that men can replenish their sperm supplies almost indefinitely, but a woman is born with her lifetime supply of eggs. However, a new study may turn this old idea upside down. Scientists in London have discovered that a cancer drug may have the ability to do the impossible: trigger the development of a new egg. If this outcome can be repeated, it could mean a second chance at fertility for women around the world.

The study, led by researchers from the University of Edinburgh in Scotland, found that a cancer drug called ABVD caused new eggs to be produced in the ovaries of young women who were given the drug as part of their cancer treatment, The Guardian reported. According to lead study author Professor Evelyn Telfer, it’s too early for the drug to become a part of any fertility treatments just yet, but the unexpected findings suggest that women may not have to accept their eggs as a set amount, but rather something that may be replenished.

The study was originally designed to better understand why ABVD, unlike other cancer treatments, did not affect women’s fertility. However, in the course of the research, the team noted that many of the women taking ABVD had far more eggs than normal for females of their age — double to four times the amount expected, The Guardian reported.

Although, it's not entirely clear as to whether the drug led to the increase in eggs in these women, according to Telfer, the sheer number of excess eggs suggests the eggs are newly formed and had not been inside the women for the duration of their lives.

Read: Infertility Impacts 1 in 8 Women And Only Half Seek Medical Attention

“We have no other explanation than that new eggs have been formed,” explained Telfer, The Guardian reported.

At the moment, there are many unanswered questions; for example, it’s still not clear if these new cells are even functional and have the ability to be fertilized. In addition, it’s also not clear where the eggs came from. According to The Guardian, it’s possible the eggs were already there and rose to the surface when the ovary was stressed by the treatment, or that egg follicles split into two or more parts due to damage from the treatment. Still, the finding hints that our understanding of female reproduction may be limited, and suggests that infertility could be a reversible diagnosis.

Source: McLaughlin M, Kelsey TW, Wallace WHB, Anderson RA, Telfer EE. Non-growing follicle density is increased following adriamycin, bleomycin, vinblastine and dacarbazine (ABVD) chemotherapy in the adult human ovary. Human Reproduction . 2016

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