07/10/2012 04:44 pm ET

Breast Cancer Not Strongly Linked To Fertility Treatment, Study

Even before E! host Giuliana Rancic's breast cancer diagnosis shone a spotlight on it, researchers had questions about a possible link between fertility drugs and increased risk for the disease.

Now, a new study from researchers with the National Institutes of Health suggests that it does not. It finds that overall, ovulation-inducing fertility treatments like Clomid and follicle stimulating hormone (FSH) do not significantly increase a woman's odds of developing breast cancer.

The research did, however, reveal differences in cancer risk after infertility treatment based on whether or not the patient became pregnant for a significant amount of time after treatment.

"I think the bottom line for patients is that this study should be reassuring," Dr. Marcelle Cedars, director of the division of reproductive endocrinology and infertility at the University of California, San Francisco -- who did not do research for the study -- told The Huffington Post.

"While it showed an increased risk in patients who use ovulation-inducing fertility drugs and got pregnant compared to women who didn't get pregnant, that rate was still not higher than the general population," Cedars said. "So even the worst group did no worse than women who didn't use fertility drugs at all."

To probe the possible link between breast cancer and fertility treatments, researchers compared sisters who'd developed breast cancer before the age of 50 with those who were cancer-free.

They found that women who had taken fertility drugs but did not get pregnant had a slightly lower risk of developing breast cancer, whereas women who stayed pregnant for at least 10 weeks had a slightly elevated risk.

Overall, their risk was still on par with women who'd never taken fertility drugs.

In an editorial accompanying the study, which appeared in the Journal of the National Cancer Institute, researcher Louise Brinton -- a senior investigator with the National Cancer Institute's division of Cancer Epidemiology and Genetics -- said it is difficult to know why getting pregnant after taking fertility drugs appeared to influence a woman's breast cancer risk.

The study's authors suggest that taking the medications may result in abnormally high exposure to ovarian hormones early on in pregnancy, which can affect breast cells. But Brinton said it might simply be that patients who were able to get pregnant had greater exposure to the drugs, thus upping their risk, albeit only slightly.

Other studies have offered similar news about infertility drugs and breast cancer risk. One study that came out of Denmark in 2007 looked at more than 54,000 women with infertility problems for several years and found no strong link between breast cancer risk and use of fertility drugs, though its authors did call for longer-term follow-ups.

"That's a pretty good source of data, and it doesn't show an association between the use of fertility medicine and development of breast cancer," said Dr. James Grifo, director of the New York University Fertility Center. "It's in big numbers, over long periods of time. That's going to be the study that's the most impactful."

Grifo cautioned that neither the earlier study nor the new research can effectively eliminate all concerns about a tie between fertility drugs and breast cancer risk. However, in his opinion, the new findings are promising.

"Potentially there's a risk, but it's not a very big risk," Grifo said. "Is it worth [it]? That's a personal decision that patients need to make with informed consent."