Infertility drugs don't increase breast cancer risk, study says

The use of infertility drugs doesn’t increase the risk of getting breast cancer, according to a new study published Friday.

Researchers tracked more than 9,800 women who took the fertility drugs Clomid or gonadotropins to treat infertility between the years 1965 and 1988, and found that 749 of them developed breast cancer by 2010, which was not a significant difference from those not taking the drugs.

"We wanted to evaluate the long-term relationship of fertility medications and breast cancer risk after controlling for other factors that have been shown to be correlated with both breast cancer risk and use of those drugs," Louise A. Brinton, chief of the Hormonal and Reproductive Epidemiology Branch at the National Cancer Institute (NCI) in Bethesda, Md. and lead author of the study, said in a release. "Overall, our data show that use of fertility drugs does not increase breast cancer risk in this population of women, which is reassuring."

The study was published Friday in the journal Cancer Epidemiology, Biomarkers & Prevention, which is published by the American Association for Cancer Research.

The researchers did find that a small number of women who took 12 or more cycles of Clomid had 50 percent higher chance of developing breast cancer than women who had never taken a fertility drug. However, 12 cycles of Clomid is a much higher dosage than the three to six cycles of the drug that are prescribed today, the authors wrote.

In addition, women who were still unable to get pregnant after taking either Clomid or gonadotropins had nearly twice the risk of developing breast cancer as women who had never taken either drug. But that increased breast cancer risk is likely tied to the infertility problems themselves, the researchers said.

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

Previous studies about women’s increased risk of getting ovarian cancer or breast cancer as a result of taking certain fertility drugs have yielded conflicting results, the authors wrote. But they said the findings of this study offered “generally reassuring results” about long-term effects of taking fertility drugs that stimulate ovulation.

And with improved outcomes in assisted reproductive technologies such as in-vitro fertilization (IVF), and with egg-freezing no longer considered to be an experimental procedure by the American Society for Reproductive Medicine, more women may be choosing to treat their infertility problems with such drugs.

But the researchers did caution that the average age of onset of breast cancer among the women who did develop it was fairly young.

"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," Brinton said. "However, the women in our study who developed breast cancer were on average only 53 years old, which is still young in terms of when we usually expect breast cancers to develop.”