FRIDAY, July 6, 2012 (HealthDay News) -- Whether or not a woman becomes pregnant while on fertility drugs may affect her odds for breast cancer later on, a new study suggests.
However, experts who reviewed the study said it has flaws and is far from conclusive.
In the study, published July 6 in the Journal of the National Cancer Institute, women using ovulation-stimulating fertility drugs who were unable to get pregnant for at least 10 weeks had a lower risk of the disease than women who have not taken the drugs, the U.S. study found.
On the other hand, the odds of breast cancer rose for women who became pregnant for at least 10 weeks after taking the fertility drugs, when compared to women who were unsuccessfully treated with these drugs.
However, the risk for women who became pregnant while on fertility drugs rose only high enough to put it on par with women who had never taken fertility drugs, the researchers noted.
The researchers, led by Chunyuan Fei, at the U.S. National Institute of Environmental Health Sciences, examined women diagnosed with breast cancer before the age of 50, as well as their sisters who did not have the disease, over the course of two years.
"Our data suggest that exposure to a stimulated pregnancy is enough to undo the reduction in [breast cancer] risk associated with a history of exposure to ovulation-stimulating drugs," the authors wrote.
The study's authors pointed out that the study was limited by its reliance on the participants' self-reported fertility drug usage, and a lack of information on each woman's specific diagnosis for infertility. The study is also complicated by the fact that it focuses on women who developed breast cancer before the age of 50, and these tumors are often associated with genetic factors.
In an accompanying editorial, Louise Brinton, of the division of cancer epidemiology and genetics at the U.S. National Cancer Institute, noted that the effects of one fertility drug are similar to an established drug long used to prevent cancer -- a finding that could help explain the study results.
Still, Brinton believes more research is needed to understand the link between breast cancer risk and fertility drugs.
Two other experts took issue with the study's methodology.
"It is hard to draw a conclusion as to whether or not treatment for infertility increases the risk of breast cancer from this study," said Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City. She said these types of cases-vs.-control group studies are somewhat unreliable, and she pointed out that while some prior studies looking at fertility drugs and breast cancer have found a link, others have not.
"One of the ways to reach a better conclusion would be the creation of a national data bank where information on women undergoing treatment is entered and updated as time progresses," Bernik said. "This is an important question to answer, and better methods of obtaining the information need to be established."
For his part, Dr. Paul Tartter, a breast surgeon at St. Luke's & Roosevelt Hospital Center in New York City, noted that "previous studies have not found an increased risk [of breast cancer for women on fertility treatment]. Only one previous study noted a slightly increased risk, which was not statistically significant."
He also took issue with the choice of control group included in the study.
"The control group for these women should be women of the same age who became pregnant without IVF -- they did not use the correct control group. Using the patients' sisters is irrelevant," Tartter explained. Furthermore, "the cases had significantly younger age at menarche [onset of menstruation] and older age at first birth, both well-known risk factors for breast cancer. Nowhere in this study did they control for these differences."
More information
The American College of Obstetricians and Gynecologists provides more information on infertility treatments.
