Clinical Trial Registration and News
A 30-year study has found that fertility drugs used to stimulate ovulation do not appear to increase breast cancer risk. The findings branch away from previous studies that have linked these types of drugs to female cancers.
“There were a couple of studies in the early 90s that suggested a very large increase in ovarian cancer risk for women who had taken fertility drugs,” said Dr. Louise A. Brinton, chief of the Hormonal and Reproductive Epidemiology Branch at the National Cancer Institute, who added that a number of subsequent studies have been unable to confirm this relationship.
The concerns originally stemmed from the fact that fertility drugs increase estrogen levels, which might make women more likely to develop endometrial cancers. However, Brinton says that long-term research has found no definitive link between medications for infertility and increased risk for breast, ovarian or endometrial cancers.
The study started out with data from over 12,000 women evaluated for infertility between 1965 and 1988 at various sites throughout the country. Follow-ups continued until 2010, at which point 9,892 were eligible for the study. According to researchers, 749 of these women were eventually diagnosed with breast cancer. Of these, researchers had access to the medical documentation of 696 women. This data revealed that 77 percent of these women had invasive breast cancer.
“These types of studies are complicated to conduct because of the need to account for other predictors of cancer risk, including various causes of infertility and whether or not a woman is able to conceive,” said Brinton.
Brinton and her team did observe an increased risk among a small group of women who received 12 or more cycles of a drug called clomiphene. Women in this group were roughly 1.5 times more likely to develop breast cancer when compared to women who’d never taken fertility drugs. These cycles were given at dosages that are much higher than what is currently prescribed. Under today’s standards, clomiphene is typically administered in three to six cycles at doses up to 100 milligrams. Some women in the study received doses of up to 250 milligrams for many years.
Researchers also observed an increased breast cancer risk in a sub-group of women who were unable to conceive after taking clomiphene and gonadtropins. When compared to study participants who’d never taken these drugs, these women had nearly twice the risk of developing breast cancer. According to Brinton, it’s difficult to determine if these increased risks were necessarily due to drug effects. Researchers say it’s possible that they were caused by more resistant infertility.
Brinton advises that study participants continue to be monitored for future breast cancer. She also says that more research is needed to determine the risks associated with fertility drugs that are currently used with in vitro fertilization.
By Marianne Hayes