A new federally funded study of possible links between certain fertility drugs and breast cancer risks has both good and bad news for women.
The study, published in the Journal of The National Cancer Institute, found that women who took the drugs and did not get pregnant had a slightly lower risk of developing breast cancer before age 50. But those who took the drugs and reported a pregnancy lasting 10 weeks or more had a slightly greater cancer risk – but it was about the same as the risk faced by women who never took fertility drugs at all.
The study, funded in part by Susan G. Komen for the Cure, noted some concerns have been raised over ovulation-stimulating fertility drugs that temporarily elevate estrogen levels in women, which can play a role in breast cancer. While some studies have found increased breast cancer risk following infertility treatment, other analyses have been inconclusive.
For the new study, Chunyuan Fei and colleagues with the National Institute of Environmental Health Sciences studied more than 1,500 pairs of sisters – including 1,400 women diagnosed with breast cancer before age 50 and 1,600 of their sisters who never developed the disease – from 2008 to 2010.
The researchers compared the women’s use of fertility drugs and whether the treatments had resulted in a pregnancy lasting at least 10 weeks.
The researchers found that women who had used fertility drugs but did not conceive a pregnancy lasting 10 weeks or more had a slightly reduced risk of breast cancer, compared to women who did not use fertility drugs. But women who took fertility drugs and conceived a 10-plus week pregnancy had a greater risk of breast cancer compared to women who had been unsuccessfully treated, but that risk was about the same as women who had never undergone such treatments.
The authors note a few limitations of the study, including the reliance on self-reported fertility drug usage, and lack of data on specific diagnosis for infertility.
Researchers suggested the reduced risk tied to fertility drugs may be related to the fact that one of the medications, clomiphene, is a selective estrogen receptor modulator similar to tamoxifen, used to prevent breast cancer. On the other hand, increased risk seen in successfully treated women may be related to the increased exposure to ovarian hormones.