WOMEN who go through in vitro fertilisation (IVF) early in life are at a higher risk of developing breast cancer compared to those who don't undergo the treatment, according to a new study.
But the findings, based on a study of more than 21,000 women, cannot determine whether IVF contributed to the cancers or whether something else could explain the risk.
"I don't think it's a huge increased risk that you should worry or panic (about)," said Louise Stewart, the study's lead author and a researcher at the University of Western Australia in Crawley.
She added, however, that the findings did show a link between the two and doctors should keep that in mind.
For the study, Stewart and her colleagues collected information on 21,025 women between the ages of 20 and 40 who went through fertility treatment at the hospitals of Western Australia between 1983 and 2002.
They were able to piece together enough data to follow the women for some 16 years to see if they developed breast cancer.
Roughly 1.7pc of the 13,644 women who only used fertility drugs without IVF ended up developing breast cancer by the end of the study.
That figure was about 2pc for women who used fertility drugs and underwent IVF -- a difference that researchers said wasn't statistically significant.
When they divided the women into different age groups, though, that changed.
Women who started taking fertility drugs around their 24th birthday and went through IVF had a 56pc greater chance of eventually developing breast cancer compared with those in the same age group who only went through fertility treatments without IVF.
But there was no increased risk for women who started fertility treatments when they were about 40 regardless of whether they had IVF or not.
Stewart said that a possible reason that younger women see an increased risk of breast cancer is that they are exposed to higher levels of circulating oestrogen during their cycles of IVF treatment.
"The development of breast cancer is linked to oestrogen exposure and the longer one is exposed, the greater the risk," said Linda Giudice, president-elect of the American Society of Reproductive Medicine.