Women who took Clomid during treatment for infertility are not at increased risk for developing breast cancer, even if they took the drug 30 years ago, according to a new study. The study's lead researcher says the findings of her study are "reassuring."

Clomid (clomiphene citrate) and gonadotropins (hormones) are often given to women during infertility treatment to stimulate the ovaries to produce eggs. Along with its use, however, has been the fear the drug would increase a woman's long-term breast cancer risk. The study analyzed the medical records of 12,193 women who were evaluated for infertility between 1965 and 1988 at five fertility centers across the United States.

Dr. Louise A. Brinton led the study. She is chief of the Hormonal and Reproductive Epidemiology Branch of the National Cancer Institute in Bethesda, Maryland. She says of the study's findings, "Overall, our data show that use of fertility drugs does not increase breast cancer risk in this population of women, which is reassuring."

Follow-up study of the 12,000+ women initially evaluated for fertility treatment produced 9,892 in 2010 who were eligible for the Brinton study. Since taking the fertility drugs years ago, 749 developed breast cancer but medical records were available for analysis for only 696 of them. Of these, 536 women had invasive breast cancers. The incidence of breast cancer in this group was not significantly different from the rate of breast cancer in the general population of US women.

Within the group of breast cancer patients, there were small subsets of women found to have risks for breast cancer slightly higher than the general population never taking fertility drugs:


  • Women who took clomiphene for 12 or more cycles of fertility treatments were found to be 1.5 times more likely to develop breast cancer.
  • Women who underwent infertility treatments using clomiphene and gonadotropins but never became pregnant were twice as likely to develop breast cancer.

Current dosage protocol for clomiphene is a maximum of 100 milligrams (mg) covering three to six cycles. When the women in the study took it, doses of up to 250 mg were not uncommon and some women took it for years.

Brinton says the small group of women at increased risk for breast cancer after taking Clomid and gonadotropins may have developed the disease as a result of infertility, not the drug therapies. She calls for continued monitoring of all the women in the study to assess risk over an even longer period of time.

Source: Brinton, Louise A, et al. "Long-term Relationship of Ovulation-Stimulating Drugs to Breast Cancer Risk." Cancer Epidemiology, Biomarkers & Prevention. American Association for Cancer Research. Apr 23, 2014. Web. Apr 24, 2014.