Fertility treatment does not increase a woman's risk of developing breast cancer, according to a study of more than 25,000 women with fertility problems in the Netherlands.
The study will help to reassure patients concerned that the powerful doses of hormones that are part of fertility treatment might put them at risk of developing cancer in the future.
At the beginning of an IVF treatment cycle, women are given a course of hormone drugs to stimulate their ovaries to produce more eggs than usual so that clinicians can produce several fertilised embryos in vitro.
The treatment causes large spikes in oestrogen levels in the body. In theory this could promote the development of breast cancer, which is sensitive to the hormone.
The Dutch study, carried out by Dr Alexandra van den Belt-Dousebout at the Netherlands Cancer Institute in Amsterdam, examined patient records from all 12 IVF clinics in the country between 1980 and 1995.
Her team compared 18,970 women who had had at least one cycle of IVF treatment and 7,536 other women with fertility problems who had not received fertility treatment. They matched these patients to records in the National Cancer Registry to establish whether they had gone on to develop breast cancer.
Of the 378 women who developed breast cancer, 266 were in the IVF group and 112 were in the non-IVF group. After adjusting for known risk factors such as age, the number of children the women already had, the age they began menstruating, family history of breast cancer and body mass index, the team found no statistical difference between the two groups, suggesting that IVF treatment does not increase a woman's chances of developing breast cancer.
Van den Belt-Dousebout presented her results at the American Society for Reproductive Medicine in San Francisco.
"From 10 years after treatment breast cancer risk was moderately increased in the IVF group but also in the non-IVF group, compared to the general population," van den Belt-Dousebout and her colleagues wrote in their presentation, "This may be explained by a lower number of children compared to the general population."
Having children is known to reduce the risk of breast cancer in women.
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