Use of Fertility Drugs May Raise Breast Cancer Risks

Fertility drugs use may increase risks for breast cancer, according to a new study conducted by researchers from the National Institute of Environmental Health Sciences in Bethesda, Maryland.

The study, said emaxHealth, found that women who took fertility drugs and who did not become pregnant and maintain a pregnancy for at least 10 weeks, had a statistically significant reduced risk for breast cancer when compared to nonusers. Meanwhile, women who used fertility drugs and who became pregnant for at least 10 weeks, had a statistically significant increased breast cancer risk, versus unsuccessfully treated women, which is comparable to nonusers. Study results appear online in the July 6th issue of the Journal of the National Cancer Institute. The research team was led by Chunyuan Fei, PhD.

The researchers pointed out that ovulation-stimulating fertility drugs temporarily elevate a woman’s estrogen levels, which is known to have a significant role in breast cancer. The team indicated that some studies revealed an increased breast cancer risk following infertility treatment; however, those studies have been deemed inconclusive, said emaxHealth. This new study reviewed data from the Two Sister Study, a case–control study in which sisters—one diagnosed with breast cancer before age 50 and one not diagnosed with breast cancer—were studied. Of the 1,422 women diagnosed with breast cancer and their breast-cancer-free sisters, 288 women reported using fertility drugs such as Clomid (clomiphene citrate), follicle-stimulating hormone, or both, explained emaxHealth.

Clomid may also be sold under the brand name Serophene; is the most commonly prescribed fertility drug; and is used to induce ovulation (egg production) in women who do not produce ova (eggs), but who wish to become pregnant. Clomid is in a class of medications called ovulatory stimulants and works similarly to estrogen, the female hormone that causes eggs to develop in the ovaries and be released.

In an accompanying editorial, Louise A. Brinton, PhD wrote that the reduced risk might be related to Clomid only. Clomid is a selective estrogen-receptor modulator that is similar to tamoxifen, a “well-established chemopreventative agent.” Brinton added that only a few study participants were treated with just a follicle-stimulating hormone, according to emaxHealth, which noted that Dr. Brinton is affiliated with the Hormonal and Reproductive Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute Rockville, Maryland.

According to the study authors, “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,” adding that “there are known hormonal effects of ovarian stimulation in the first trimester of pregnancy” and this raises risks for breast cancer.

emaxHealth wrote that, based on the study’s findings, women who take fertility drugs and who achieve a successful pregnancy, experience breast cancer risks that are not higher than what is seen in women who never took fertility drugs. Risks may be lowered if the drugs are taken and a so-called “successful pregnancy” is not achieved. Risks may also be reduced if fertility drugs are taken and a pregnancy is not achieved.

Fertility drugs have also been linked to birth defects, including a large study that reviewed data in South Australia and was published in The New England Journal of Medicine. Clomid use was associated with increased risks for birth defects based on research published online in the journal Human Reproduction in which a significant association was found with nine types of birth defects following Clomid use.

A 2003 study (Reefhuis, et al) discovered a 280 percent increased risk of craniosynostosis; while another study published in 2006 (Wu, et al) found a 10-fold increased risk for spina bifida. A separate 2006 article (Meijer, et al) revealed a 508 percent increased risk of penoscrotal hypospadias.