Type of evidence: Observational
Researchers report no increased risk of womb cancer or invasive breast cancer after assisted reproduction in a study of over 250,000 British women published by The BMJ today.
Small increased risks of non-invasive breast and ovarian tumours were found, but the researchers say these results may not be due to the treatment itself and require further investigation.
Assisted reproduction is practiced worldwide and more than five million children have been born as a result. But it usually involves exposure to high levels of hormones, which can carry an increased risk of breast, endometrial (womb), and ovarian cancers.
Results of previous studies on risks of reproductive cancers in women who have undergone assisted reproduction are inconsistent.
So a team led by Professor Alastair Sutcliffe at UCL Great Ormond Street Institute of Child Health in London, set out to investigate the risks of ovarian, breast and womb (corpus uteri) cancer in women who have had assisted reproduction.
Using Human Fertilisation and Embryology Authority (HFEA) records, they identified all women who had assisted reproduction in Britain between 1991 and 2010 and then linked this information to national cancer records.
In total, 255,786 women were followed up over an average of 8.8 years. Average age at first treatment was 34.5 years and women had an average of 1.8 treatment cycles.
Cause of infertility involved at least one female factor in 111,658 (44%) women. Infertility was unexplained in 47,757 (19%) women, and was due only to male factors in 84,871 (33%).
The team found no overall increased risk of breast cancer or invasive breast cancer associated with assisted reproduction, compared with the general population.
An increased risk of non-invasive (in situ) breast cancer was detected (absolute excess risk of 1.7 cases per 100,000 person years), which was associated with an increasing number of treatment cycles.
An increased risk of ovarian cancer, both invasive and borderline, was also detected (absolute excess risk of 5 cases per 100,000 person years), but this was limited to women with other known risk factors, suggesting this may be due to underlying patient characteristics, rather than assisted reproduction itself.
The researchers found no overall increased risk of womb cancer.
They point out that this is an observational study, so no firm conclusions can be drawn about cause and effect, and they outline some limitations that could have affected the results. However, strengths include the large sample size and long follow up period, which enabled them to adjust for potentially influential factors.
And they conclude that ongoing monitoring of these important outcomes in this ever growing population is essential.