Women who go through in vitro fertilization (IVF) early in life are at a higher risk of developing breast cancer compared to those who don't undergo the treatment, according to an Australian study.
But the findings, based on a study of more than 21,000 women and published in the journal Fertility and Sterility, 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 1.7 percent 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 two percent 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 56 percent greater chance of eventually developing breast cancer compared to 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 years old, regardless of whether they had IVF or not.
Stewart told Reuters Health that a possible reason that younger women see an increased risk of breast cancer is that they are exposed to higher levels of circulating estrogen during their cycles of IVF treatment.
"The development of breast cancer is linked to estrogen exposure and the longer one is exposed, the greater the risk," said Linda Giudice, president-elect of the American Society of Reproductive Medicine, in a statement.
"In an IVF cycle there is a short, but significant elevation in circulating estrogen, and whether this is linked to the observations found in the study is not clear at this time."
Stewart added that another explanation could be that younger women who undergo IVF may be different in some significant way from those who only have other types of fertility treatment.
"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," she said.
She emphasized that this is just speculation, adding that the data used in the study didn't include information about the women's causes of infertility - and that the current study's results need to be confirmed by future research.
Pauline Cafferkey was admitted to the Royal Free Hospital after falling ill on her return from Sierra Leone, where she had been working for the charity Save the Children
"Both for malaria and AIDS we're seeing that the tools that will let us do 95 to 100 percent reduction, those tools will be invented during this 15-year period", said Gates.
A five-year-old boy died from the virus in the southern Assiut province
"The probability of global catastrophe is very high," says advocacy group
Nigeria H5N1 bird flu now in 7 states, suspected in 140,000 birds
Using video feedback-based therapy to help parents understand and respond to their baby's early communication style might help modify emerging autism symptoms
The unprecedented outbreak has so far killed more than 8,400 people, overwhelmingly in Liberia, Guinea and Sierra Leone.
Obama launched a new precision medicine initiative to bring closer to curing diseases like cancer and diabetes
Britain has one of the highest persistent tuberculosis (TB) rates in western Europe
Nigeria, Africa's most populous country and biggest economy, was the continent's first country to detect bird flu in 2006
The data showed that the 10 warmest years since records began in the 19th century had occurred since 1997
Nearly 85 percent of births are delivered by C-section in Brazil's private hospitals
Sea level rise is gnawing away at shores from Miami to Shanghai. In cities such as Jakarta, the rise is aggravated by big local subsidence.
The migration has occurred during the last one to three generations of the predators, or between 15 and 45 years
The project was inspired by similar initiatives in the Amazon region of Latin America