Women who take fertility drugs and do not get pregnant have a slightly reduced risk of developing breast cancer before age 50; however, those who do experience a pregnancy lasting 10 weeks or more have a slightly increased risk—one that is comparable to the risk of women who never took fertility drugs, according to the results of a study published in the Journal of the National Cancer Institute.
Breast cancer is the most commonly diagnosed type of cancer (other than skin cancer) in U.S. women. Each year, roughly 227,000 women are diagnosed with breast cancer and close to 40,000 die of the disease. Researchers continue to investigate factors that may increase or reduce the risk of breast cancer.
Fertility drugs have come under scrutiny because they stimulate hyper-ovulation, meaning they cause a woman’s body to produce more eggs. The additional eggs increase estrogen levels and estrogen has been linked to an increased risk of breast cancer.
To examine the relationship between fertility drugs and breast cancer risk, researchers conducted the Two Sister Study, a sister-matched case-control study that studied pairs of sisters. The study included 1,422 women under age 50 diagnosed with breast cancer between 2008 and 2010 and 1,669 of their sisters who had never had breast cancer.
A total of 288 women reported using one or both of the ovulation-stimulating fertility drugs clomiphene citrate (CC) and follicle-stimulating hormone (FSH) at some point and 141 women reported a pregnancy that lasted 10 weeks or more after taking the drugs. Overall, women who had taken fertility drugs had a slightly decreased risk of breast cancer compared with those who had never taken the drugs, but this risk was not considered statistically significant. Women who used fertility drugs but did not get pregnant had a statistically significantly reduced risk of breast cancer compared with non-users. Women who used fertility drugs and conceived a pregnancy that lasted 10 or more weeks showed a statistically significantly increased risk of breast cancer compared with their counterparts who took fertility drugs and did not get pregnant; however, this risk was not increased compared with women who had never used fertility drugs.
The researchers noted that there was no cause for alarm because even in the group with the increased risk after pregnancy, the risk was not higher than that of the general public.
The researchers concluded that using fertility drugs does not increase the risk of breast cancer and in fact, exposure to ovulation-stimulating fertility drugs may even reduce the risk in women who do not experience pregnancy that lasts 10 weeks or more.
Fei C, DeRoo LA, Sandler DP, Weinberg CR. Fertility drugs and young-onset breast cancer: Results from the Two Sister Study. Journal of the National Cancer Institute. Published early online July 6, 2012. doi: 10.1093/jnci/djs255