Fertility drugs may lower breast cancer risk

Women using fertility drugs who did not conceive a 10-plus week pregnancy had a reduced risk of breast cancer compared to nonusers, according to a study.

Women using the drugs who conceived a 10-plus week pregnancy had an increased risk of breast cancer compared to unsuccessfully treated women, but a comparable risk to nonusers, researchers reported July 6 on the website of the Journal of The National Cancer Institute.

Ovulation-stimulating fertility drugs temporarily elevate estrogen levels in women, and estrogen is known to play a role in breast cancer, the researchers wrote in background information. Although some studies have reported an increased breast cancer risk following infertility treatment, other analyses have been inconclusive.

Chunyuan Fei, PhD, and colleagues with the National Institute of Environmental Health Sciences conducted a case-control study that compared women diagnosed with breast cancer under age 50 with their breast cancer-free sisters. They looked specifically at fertility-drug exposure according to whether or not it had resulted in a pregnancy lasting at least 10 weeks.

“Our data suggest that exposure to a stimulated pregnancy is enough to undo the reduction in risk associated with a history of exposure to ovulation-stimulating drugs,” the authors wrote. They noted a few limitations of the study, including the reliance on self-reported fertility drug usage and lack of data on specific diagnosis for infertility.

Results interpretation

In an accompanying editorial, Louise A. Brinton, PhD, of the Division of Cancer Epidemiology and Genetics at the National Cancer Institute, wrote that the findings of the study are hard to understand in the context of previous studies with results ranging from a lowered risk to a higher risk to no relationship between the drugs and the risk of early onset of breast cancer.

Brinton said the reduced overall risk associated with drug usage may be related to the fact that one of the drugs, clomiphene, is a selective estrogen receptor modulator similar to tamoxifen, an established chemo-preventative. On the other hand, increased risk seen in successfully treated women may be related to the increased exposure to ovarian hormones, as well as “the dual effect of pregnancy on breast cancer risk, namely a short-term transient increase that dissipates with time and eventually leads to a long-term risk reduction,” Brinton wrote.

Another complicating factor in interpreting the study’s results is its focus on women who developed breast cancer before age 50, which is more often associated with genetic factors than are breast cancers diagnosed at a later age, she noted.

Brinton concluded that additional research is needed to understand these associations: “Because of such complexities, results from individual investigations must be cautiously interpreted and weighed against the considerable benefits associated with fertility drug usage, including a high probability of carrying pregnancies to term, which can lead to substantial long-term reductions in breast cancer risks.”

To read the study abstract and access the study via subscription or purchase, visit http://bit.ly/LJdCXX.

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