Women who undergo IVF treatment in their 20s could be more likely to develop breast cancer in later life, a University of Western Australia study has found.
But the researchers have as yet been unable to confirm a direct causal relationship between the two or whether something else caused the cancer.
Research assistant professor Louise Stewart led the study that looked at the records of 21,025 women aged 20 to 40, who underwent fertility treatment between 1983 and 2002.
Overall, they found 1.7 percent of the women who underwent fertility treatment without IVF developed breast cancer, compared with two percent of women who had both fertility treatment and IVF. The researchers said the 0.3 percent difference was negligible.
However, when they divided the women into age groups, they found women who started taking fertility drugs when they were 24 and went through IVF had a 56 percent greater chance of developing breast cancer, compared with women of the same age who only had fertility treatment.
In contrast, women who started fertility and IVF treatment in their 40s had no increased risk.
Stewart told Reuters Health the increased risk of breast cancer in younger women could be due to the higher levels of circulating oestrogen they're exposed to during IVF. It could also be due to younger women being different in some way to people who undergo other fertility treatment, and therefore IVF would not be the specific cause.
"If, for example, younger women who had IVF were more likely to have a specific cause of infertility, and this was related to an increased risk of breast cancer, then it would appear that IVF was related to breast cancer when in fact it was the type of infertility that was more common in women who had IVF," Stewart explained.
The study did not include information about the women's causes of infertility, so further research needs to be done.
"I don't think it's a huge increased risk that you should worry or panic [about]," Stewart said.
The study was published in Fertility and Sterility.