Fertility Drugs Do Not Raise Breast Cancer Risk, Study Finds

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Women who took a fertility drug called Clomid don’t have any higher risk of breast cancer, even 30 years later, than women who did not, a new study shows.

The findings should reassure women worried that they would pay down the road for having taken the drug, which stimulates the production of eggs.

“Overall, our data show that use of fertility drugs does not increase breast cancer risk in this population of women, which is reassuring,” says Louise Brinton, who heads research on hormone-related cancer at the National Cancer Institute.

In 2009, another team of researchers showed the drugs also did not appear to raise the risk of ovarian cancer.

It is a hard risk to study, because women who are infertile have a higher risk of cancer, so it’s been difficult to show whether the drugs raise the risk. Brinton’s study, published in the journal Cancer Epidemiology, Biomarkers and Prevention, shows women who did not conceive despite taking fertility drugs had nearly twice the risk of breast cancer compared with women who did not take fertility drugs.

And women who took 12 or more cycles of Clomid, known generically as clomiphene, also had a small increased risk, the study of 9,800 women showed.

“The observed increase in risk for these small subsets of women may be related to persistent infertility rather than an effect of the medications,” said Brinton. “Nevertheless, these findings stress the importance of continued monitoring of women who are exposed to fertility drugs.”

Doctors now limit clomiphene to three to six cycles at doses far lower than what were given in the past.

“Given the high doses of drugs received by our study participants and the lack of large increases in breast cancer risk many years after exposure, women previously exposed to such drugs should be reassured by these findings,” said Brinton.