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Fertility drugs and breast cancer risk

Robin Wulffson MD's picture
fertility drugs, breast cancer, Clomid, follicle-stimulating hormone

A new study has presented an interesting finding: women who took fertility drugs and did not conceive a 10-plus week pregnancy had a reduced risk of breast cancer; however, women, who conceived a 10-plus week pregnancy had an increased risk of breast cancer. Researchers from the National Institute of Environmental Health Sciences in Bethesda, Maryland published their findings online on July 6 in the Journal of the National Cancer Institute.

A research team led by Chunyuan Fei, PhD noted that ovulation-stimulating fertility drugs temporarily elevate estrogen levels in women, and estrogen is known to play an important role in breast cancer. They added that some studies have reported an increased breast cancer risk following infertility treatment; however, others have been inconclusive. The new study accessed data from the Two Sister Study, which is a case–control study (one sister diagnosed with breast cancer before age 50, one without). Of the 1,422 women with breast cancer and their corresponding breast-cancer-free sisters, 288 women reported using fertility drugs (clomiphene citrate (Clomid), follicle-stimulating hormone, or both).

The researchers found that women using fertility drugs who did not conceive a 10-plus week pregnancy were at a statistically significant reduced risk of breast cancer compared to nonusers. In contrast, women using the drugs who conceived a 10-plus week pregnancy had a statistically significant increased risk of breast cancer compared to unsuccessfully treated women. However, this risk was comparable to nonusers. In an accompanying editorial, Louise A. Brinton, PhD noted that the reduction might only be related to clomiphene, which is a selective estrogen-receptor modulator similar to tamoxifen, which is a “well-established chemopreventative agent.” She added that very few women in the study were treated with follicle-stimulating hormone alone. (Dr. Brinton is affiliated with the Hormonal and Reproductive Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute Rockville, MD.

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The study authors wrote: “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.” They noted that “there are known hormonal effects of ovarian stimulation in the first trimester of pregnancy” that raise breast cancer risk.

Dr. Brinton noted “These results are difficult to interpret in the context of previous studies, given that findings have ranged from reduced risks to increased risks to the absence of any relationship.” She added that the relation between fertility drugs and breast cancer risk is complex and, as a consequence, “results from individual investigations must be cautiously interpreted.” She stressed that fertility drug use has “considerable benefits.” These include “a high probability of carrying pregnancies to term, which can lead to substantial long-term reductions in breast cancer risks.” She notes that there is also a well-documented “dual effect” of pregnancy on breast cancer risk. There is a “short-term transient increase that dissipates with time” and eventually leads to the above-mentioned long-term risk reduction.

Take home message:
According to this study, if you take fertility drugs and achieve a successful pregnancy, your risk of breast cancer is no higher than if you did not take these medications. It may be lower if you take the drugs and do not achieve a pregnancy. If you have a strong family history of breast cancer (mother or sister), you might weigh the findings of this study against whether you should take fertility medication. Your age is a factor: women in their late 30s and 40s are less likely to conceive with fertility drugs.

Reference: Journal of the National Cancer Institute

See Also:
Do vaginal lubricants impact fertility?
Reduce your breast cancer risk with exercise