May 24, 2012

expert reaction to IVF and breast cancer

In a large population-based study out of Western Australia, researchers have found that IVF is not associated with an overall increased risk of breast cancer. However, the analysis demonstrates an underlying, age-related connection in that for younger, but not older, patients there was an association between having IVF and an increased risk of breast cancer.

Nick Ormiston-Smith, Statistical Information Manager, Cancer Research UK, said:

“The incidence rate of breast cancer in women aged 20 to 24 is very low, fewer than two women per 100,000 per year, so an increase in risk of over 50 per cent would suggest less than one additional cancer per year in 100,000 women.

“Fewer than 25,000 women aged between 18 and 34 had IVF treatment in 2010. If 8,000* of these women were aged between 20 and 24, this suggests that there would be roughly one case of breast cancer every twenty years or so due to IVF treatment in 20-24 year olds in the UK.”

*The 8,000 assumes an equal number of women at each age between 18-34, however there are likely to be more women at the older end of this age group.

Dr Paul Pharoah, Reader in Cancer Epidemiology, University of Cambridge, said:

“In summary, this is a carefully conducted study but the results do need to be treated with some caution. The findings of an increase in breast cancer in younger women undergoing IVF compared to other forms of treatment for infertility may be real or they may be the result of chance or bias. If real, the absolute increase in risk is small and should not be regarded as significant by younger women considering IVF. Furthermore, this study provides no data on the long term effects of IVF on breast cancer risk and we know that the effect on risk of other factors such as pregnancy change over time.

“There are a few specific issues here that are worth comment. First, the ‘significant’ result that is presented in this paper is based on the selection of one of multiple sub-group analyses and so it is entirely plausible that this is a chance finding.

“Second, the authors have only been able to control for a limited number of factors that affect the risk of breast cancer. These factors might be systematically different between the group of women treated with IVF compared to those not treated with IVF. So, it is plausible that the findings just reflect these differences.

“However, it is also plausible that the findings are real and not the result of chance or bias. Even if we assume the results are correct, then in absolute terms the increase in risk associated with IVF in younger women is very small. A 25 year old woman in the UK has a chance of about 5 in 1000 of getting breast cancer in the next 15 years (the length of follow-up in this study). The reported relative risk was ~1.5 which would be an absolute risk of 7 cases in 1000 over fifteen years. Thus, the absolute risk increase is just 2 in 1000, which is very small.

“The authors do not report the number of children born to these women during the course of follow-up. Over a long time span (several decades), pregnancy protects against breast cancer. However, in the years immediately after pregnancy the risk of breast cancer is slightly increased. IVF itself may be mimicking the effect of pregnancy of treatment with IVF may result in more pregnancies and cause a small increase in risk in this way.

“It is entirely plausible that a short term increase in risk associated with IVF would change to a long term decrease in risk. This study would need at least twice as long a follow-up to begin to detect this effect.”

Dr Michael Jones, an epidemiologist from The Institute of Cancer Research, said:

“This is an observational study that retrospectively looked at breast cancer rates in women who had IVF and those who had other non-IVF infertility treatments. This is not a randomised-controlled trial, so although the authors have tried to minimise variables that could influence their results, there may be other factors that explain the results that they have not been able to control. This is a feature of all studies of this type, called cohort studies, but in general this study appears to be well conducted.

“The authors themselves point out their results need critical review and evaluation. A lot more work would be needed before we can say definitively whether these results are true or not.

“The most interesting new finding is that starting IVF treatment at a young age is associated with greater risk of breast cancer, but that this risk is not raised in women who first undergo IVF later in life.

“The finding that women who first underwent IVF at the age of 24 were 50 per cent more likely to develop breast cancer looks worrying, however this must be seen in the context of the very low rates of breast cancer among these women. A 50 per cent increase on low would still be low.

“It is also not clear from this study whether this increased risk continues over their lifetime or is just temporary. Breast cancer rates increase with age, so if this risk factor continued for life then it would ultimately be quite a large increased risk. However the study ran for only 16 years so it is equally possible these women’s rates of breast cancer return to normal levels in later life.

“Importantly, the study also found that there was no overall increase in breast cancer rates among women who had IVF.”

Richard Kennedy, Secretary General of the International Federation of Fertility Societies, said:

“Evidence from a range of studies over the last decade has been reassuring in terms of the risk of cancer related to infertility treatment. This latest study underlines the need for continued vigilance and international monitoring of the safety of ART and related treatments.”

‘In vitro fertilization and breast cancer: is there cause for concern?’ by Stewart et al., published in Fertility and Sterility on Thursday 24th May.