New Study Shows Fertility Drugs Do Not Increase Breast Cancer Risk, Monitoring Still Warranted

Women who took the fertility drugs clomiphene citrate (Clomid) or gonadotropins did not experience an increased risk for breast cancer compared with women who were not treated with those medications, according to a 30-year follow-up study published in the April issue of Cancer Epidemiology, Biomarkers & Prevention.

Data were collected from more than 12,000 women evaluated for infertility between 1965 and 1988 at five different locations in the United States. These patients were followed until 2010, and 9892 were deemed eligible for the study. Of those patients, 749 developed breast cancer. Researchers were only able to obtain medical documents for 696 of the 749, and 536 were found to have invasive breast cancer.

“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, PhD, MPH, chief of the Hormonal and Reproductive Epidemiology Branch at the National Cancer Institute, said in a press release. “Overall, our data show that use of fertility drugs does not increase breast cancer risk in this population of women, which is reassuring.”

An elevated risk for invasive breast cancer was observed for a small number of women in the study who were exposed to 12 or more cycles of clomiphene, and women who were unable to become pregnant after taking gonadotropins and clomiphene citrate had nearly twice the risk of women in the study that never took either medication. However, the authors of the study feel that these increases may not be related to the medications.

“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 in a press release. “Nevertheless, these findings stress the importance of continued monitoring of women who are exposed to fertility drugs.”

Under current practices, clomiphene is usually limited to three to six cycles at doses up to 100 mg, but patients in the past may have received doses up to 250 mg, oftentimes for many years, Brinton said.

“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,” she continued, “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. This cohort of women should continue to be monitored as they progress into a typical breast cancer age range; in addition, data are needed to assess the long-term effects of fertility drugs given in current practice, such as those used in conjunction with IVF.”