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Fertility Drugs Seem to Affect Breast Cancer Risk in Younger Women

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A study suggests that women younger than 50 who use fertility drugs to successfully conceive a child may have a higher risk of breast cancer. Still, this higher risk is about the same as the average woman’s risk, but higher than women who took fertility drugs and didn’t conceive.

The study was published online on July 12, 2012 by the Journal of the National Cancer Institute. Read the abstract of “Fertility Drugs and Young-Onset Breast Cancer: Results From the Two Sister Study.”

Fertility drugs stimulate the ovaries to produce more mature eggs than normal. Without fertility drugs, only one or two eggs, at most, per cycle are released. With fertility drugs, as many as eight to 10 mature eggs can be released. But using fertility drugs greatly increases the amount of estrogen in the body. This extra estrogen may stimulate the growth of hormone-receptor-positive breast cancer cells. Still, results from earlier studies on fertility drugs and breast cancer risk have been mixed, so researchers haven’t been able to make a conclusive connection.

In this study, called the Two Sister Study, the researchers looked to see if there were any associations between using two fertility drugs -- clomiphene citrate (brand name: Clomid) and follicle-stimulating hormone -- and the risk of developing breast cancer in women younger than 50.

The Two Sister Study included 1,422 women who had been diagnosed with breast cancer when they were younger than 50 and their 1,669 sisters who hadn’t been diagnosed.

The women self-reported whether they had ever taken any fertility drugs. If they had, the researchers also wanted to know:

  • the type
  • when the women started taking the drug
  • how long they had taken the drugs
  • whether the fertility drugs had led to a pregnancy that lasted 10 weeks or longer

The researchers found that women who used fertility drugs to successfully conceive had a higher risk of breast cancer compared to women who used fertility drugs and didn’t conceive. But this higher risk was the same as women who hadn’t used fertility drugs.

The women who used clomiphene citrate alone or both clomiphene citrate and follicle stimulating hormone and didn’t conceive had a lower risk of breast cancer compared to women who didn’t use any fertility drugs.

It’s important to know that while the women who used fertility drugs and didn’t conceive had a lower risk of breast cancer than the average woman, the researchers don’t think that the fertility drugs offered any protection from breast cancer. Instead, it seems likely that women who have trouble conceiving have lower levels of estrogen than average, and so have a lower risk of breast cancer.

It’s also very important to know that women who used fertility drugs and successfully conceived a child didn’t have a higher-than-average risk of breast cancer. Their risk was just higher than it was before they took the fertility drugs and conceived.

Finally, it’s also important to know that conceiving a child without fertility drugs doesn’t increase breast cancer risk.

While this study is large, it does have some limitations. The women had to remember when and for how long they took fertility drugs, so some of the information may have been misreported. We also don’t know what will happen to the women who used fertility drugs as they age. The aging process is the biggest risk factor for breast cancer. That’s because the longer we live, the more opportunities there are for genetic damage in the body. It’s not clear if taking fertility drugs earlier in life will have any effect on breast cancer risk later in life.

The study also focused on younger women diagnosed with breast cancer. In many cases, breast cancer in younger women is linked to two abnormal genes: BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two). Abnormal BRCA1 and BRCA2 genes may account for up to 10% of all breast cancers, or 1 out of every 10 cases. The researchers didn’t take into account whether the women who had been diagnosed had an abnormal breast cancer gene, which would have greatly influenced their risk of breast cancer.

If you’re having trouble conceiving a child and are considering fertility treatments, it’s good to know that this study didn’t show that fertility drugs increased the risk of breast cancer above that of the average woman.

For more information on infertility issues, you may want to visit, the website of RESOLVE: The National Infertility Association, an organization devoted to providing education and support to people with fertility problems. RESOLVE is headquartered in McLean, Virginia and has chapters across the country.

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