Despite conventional wisdom, IVF doesn't increase breast cancer risk

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A new study published the Journal of the American Medical Association could flip the previous understanding of in vitro fertilization (IVF) and breast cancer on its head.

The study says women who undergo IVF treatments are no more likely than the average woman to develop breast cancer, despite earlier indications to the contrary.

According to the New York Times, a 2012 Australian study found that some women in their 20s who used IVF were more likely to develop breast cancer than women who didn’t. The disparity was attributed to the way a woman’s hormone levels are manipulated during fertility treatment—some are increased to up to 10 times the normal level. Certain female reproductive hormones, such as estrogen and progesterone, are known to influence breast cancer.

The JAMA study followed more than 19,000 Dutch women who had received IVF treatments between 1983 and 1995 through 2013. Researchers also monitored almost 6,000 other women who had received some other kind of fertility treatment. They compared the two groups with women who hadn’t undergone any kind of fertility treatment, based on information from the Netherlands Cancer Registry.

In the overall fertility treatment-receiving group, researchers noted 839 cases of invasive breast cancer and 109 cases of in situ breast cancer within about 21 years of treatment. That rate of incidence was not significantly different between the IVF and non-IVF group, nor was it different from the general population’s rate of breast cancer incidence.

In both the IVF group and the non-IVF group, about 3 percent of women had developed breast cancer by age 55.

Even when the study authors broke apart these analyses by the age of the women at first treatment, time since treatment, current age and the age at which they had their first child, their rates of breast cancer risk were not significantly different.

In fact, women who had more treatments and then ended up giving birth saw their risk decrease. There was not significant change in risk in women who never ended up giving birth after several IVF treatments. Overall, however, the women who gave birth did end up with a slightly higher breast cancer risk, which the researchers attributed to the temporarily increased risk of breast cancer right after having a baby.

The researchers did point out that all of the women studied received their last treatment between 20 and 30 years ago—changes in procedures and IVF standards could have unknown impacts on breast cancer risk that would need to be studied in the future.