Women who undergo in vitro fertilization at a relatively young age have a higher risk of breast cancer, a new study from Australia suggests.
Researchers found that women who underwent IVF at age 24 were 1.6 times as likely to develop breast cancer as women of the same age who underwent infertility treatments but not IVF, the study showed. The link held after researchers took into account other factors known to affect breast cancer risk, such as being older at the birth of the first child, and having twins or other multiples.
When all women in the study, who were between ages 20 and 44 at the study's start, were considered, there was no overall link between undergoing IVF and breast cancer.
"The results of this study will be reassuring to women who commence IVF treatment in their 30s and 40s, because for these women, there appears to be no direct association between IVF treatment and breast cancer risk," the researchers wrote.
For younger women, "there is some cause for concern," they said, however, the link needs to be confirmed in other studies.
The findings were published online May 28 in the journal Fertility and Sterility.
IVF and cancer risk
The female hormone estrogen has long been known to fuel the growth of some types of breast cancer. The drugs used in in vitro fertilization temporarily raise a woman's estrogen levels. Levels during IVF can peak at 4,000 picograms per milliliter of blood, much higher than the 300 pg/mL seen during a normal menstrual cycle, according to the study.
Previous studies have looked at the question of whether IVF and breast cancer risk are linked, with mixed results. A 1999 study of 30,000 women in Australia published in the Lancet showed no increased risk among women who underwent IVF, compared with women in the general population.
However, in a 2008 study of 3,400 women in Israel researchers reported finding "a possible association between IVF therapy and breast cancer development," in women over age 40. On the other hand, some studies have even suggested a decreased breast cancer risk in women undergoing IVF.
A risk for younger women?
In the new study, researchers looked at information gathered on 21,000 women in Australia who underwent treatment for infertility between 1983 and 2002. Nearly 7,400 of the women underwent IVF, and the women were followed for 16 years, on average.
During the study, 384 women developed breast cancer after their infertility treatments; of these, 148 had undergone IVF, while 236 had not.
The researchers noted that the study showed an association, not a cause-and-effect link between IVF in young women and breast cancer.
While the researchers took into account several factors known to affect women's breast cancer risk, they noted that still other factors could have played a role in the findings, for example, the researchers did not have information on whether the women in the study carried the versions of the BRCA genes that have been linked with cancer.
Pass it on: A new study finds no link, overall, between IVF and breast cancer, but says that younger women who undergo IVF may face an increased breast cancer risk.