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Fertility drugs did not increase breast cancer risk
The use of clomiphene citrate or gonadotropins as a part of fertility treatment did not increase the risk for breast cancer, according to long-term study results.
“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,” Louise A. Brinton, PhD, MPH, chief of the Hormonal and Reproductive Epidemiology Branch at NCI, said in a press release. “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.”
The analysis included 9,892 women evaluated for infertility between 1965 and 1988 across five US sites. Women were followed through 2010, with a median follow-up of 30 years.
During that time, researchers identified 749 breast cancers.
Among the 38.1% of the cohort who reported ever using clomiphene citrate, researchers observed no elevated breast cancer risk (HR=1.05; 95% CI, 0.90-1.22). However, women who received 12 or more cycles were at significantly increased risk for invasive cancers (HR=1.69; 95% CI, 1.17–2.46). Researchers continued to observe this increased risk after adjustments for causes of infertility and multiple breast cancer predictors.
Among the 9.6% of study participants who used gonadotropins — primarily in conjunction with clomiphene — researchers observed inconsistent associations with breast cancer risk. However, they observed a significantly increased risk for invasive cancer among women who never became pregnant (HR=1.98; 95% CI, 1.04-3.6).
“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.”
Participants in the cohort should continue to be monitored as they enter the age bracket most typically associated with breast cancer diagnosis, the researchers wrote. Additional data are needed to evaluate the long-term effects of fertility drugs administered in current practice, including those used as part of in vitro fertilization, the researchers added.
Disclosure: One of the researchers reports consultant and advisory board roles with Agile, Bayer, Elsevier and Merck.