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."
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