The research, conducted in the Netherlands, looked at over 25,000 women who had undergone IVF treatment 21 years earlier on average. It confirms other studies, including a US study in 2013 involving 87,000 women, that showed no increased risk of breast cancer see BioNews 694.
Breast cancer can be triggered by exposure to the natural hormones oestrogen and progesterone as well as by synthetic versions of the hormones. IVF treatment involves short-term exposure to high levels of these hormones so it was important to examine the potential risk.
Dr Terri Woodard of the MD Anderson Cancer Center in Houston, Texas, who was not involved in the study, told the Washington Post: 'I was very excited about [this study].' She said that IVF patients routinely ask whether their risk of breast cancer will rise. 'Now we have a general, population-wide answer that says, no, we don't think so.'
The study, which was published in the Journal of the American Medical Association, looked at 25,108 women who had undergone fertility treatment between 1983 and 1955. Of these, 19,158 had undergone IVF treatment, and 5950 had undergone other types of fertility treatment. There was a total of 948 cases of breast cancers – a rate of three percent in both groups.
The study deliberately compared women who had undergone fertility treatment because there can be a link between infertility itself and cancer. For example, last year, a study found the women who had used assisted reproductive technologies are one-third more likely to develop ovarian cancer, but this is thought to be because the underlying cause of their infertility also raises their risk of the cancer (see BioNews 825).
The same research group, based at the Netherlands Cancer Institute in Amsterdam, also previously found no link between IVF and colon and endometrial cancer.
Although the women were followed up for an average of 21 years, their mean age at the end of the study was 54, yet the majority of breast cancers do not strike until after this. Moreover, modern IVF treatment differs significantly from the treatment in the 80s and 90s so the study results may not apply to current treatment regimes.
The study also found that women who had undergone seven or more IVF cycles had a significantly decreased risk of breast cancer than those who had undergone one or two cycles. A poor response to the first IVF cycle was also associated with a decreased risk of breast cancer.