Past research has associated the use of fertility drugs with an increased risk of breast cancer. But a new study from the National Cancer Institute indicates that this may not be the case.
The research was recently published in Cancer Epidemiology, Biomarkers & Prevention - a journal of the American Association for Cancer Research.
For women who are not ovulating properly, the use of fertility medication is often recommended. These drugs work by triggering egg production in the same way a woman's hormones would naturally.
Use of this medication alone can enable a woman to become pregnant, or it can be used alongside assisted reproductive technologies (ART), such as intrauterine insemination (IUI) and in vitro fertilization (IVF).
Whether such fertility medications increase breast cancer risk has been the subject of speculation for some time. Many studies have suggested a positive link between the two, but the researchers of this most recent study say they wanted to investigate further.
"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," explains Louise A. Brinton, chief of the Hormonal and Reproductive Epidemiology Branch at the National Cancer Institute (NCI).
Results 'reassuring' for women using fertility drugs
Researchers found that women who used fertility drugs - clomiphene citrate (Clomid) or gonadotropins - did not have an increased risk of breast cancer.
To reach their findings, the research team analyzed data from a cohort of more that 12,000 women who were assessed for infertility at five different US medical institutions between 1965 and 1988.
Of these women, 9,892 were included in the study and followed until 2010.
Breast cancer developed in 749 of the women during follow-up. The researchers were able to obtain medical documentation for 696 of the women. Of these, 536 had invasive breast cancer.
But the team found that women who took the fertility medication clomiphene citrate (brand name Clomid) or gonadotropins did not have an increased risk of breast cancer, compared with women who were not treated with these medications.
"Overall, our data show that use of fertility drugs does not increase breast cancer risk in this population of women, which is reassuring."
The team did find that women who had 12 or more cycles of clomiphene were 1.5 times more likely to develop breast cancer than women who did not use fertility medication. But Brinton notes that under current practices, women are usually limited to 3-6 cycles at doses up to 100 mg. In this study and past practices, women took doses of up to 250 mg. Some women also took these high doses for long periods of time.
Furthermore, the researchers found that women who were still unable to become pregnant after being treated with clomiphene and gonadotropins had twice the risk of breast cancer, compared with women who were not prescribed these drugs.
"The observed increase in risk for these small subsets of women may be related to persistent infertility rather than an effect of the medications," says Brinton.
"Nevertheless, these findings stress the importance of continued monitoring of women who are exposed to fertility drugs."
She notes that the women in this study who developed breast cancer were an average age of 53, which she says is still young, considering that most breast cancer cases occur in women above this age.
Women who have used fertility medication and are approaching the typical breast cancer age range should receive ongoing monitoring, according to Brinton. In addition, she says further research is needed to determine the long-term effects of fertility medication prescribed under current practices.
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Written by Honor Whiteman