There has been much debate regarding a possible link between assisted reproduction and cancer. Some cancers, particularly those of the breasts and ovaries, may be hormone responsive, and certainly hormones may be used in infertility treatment. Many hormones, such as estrogens and progesterones, are naturally produced by the body at a much higher rate during pregnancy, regardless of whether the pregnancy stemmed from IVF. There is a known relationship between an increased lifetime exposure to endogenous estrogen (for example, early menarche or late menopause) and breast cancers. Researchers are studying the relationship between breast cancer and the short-term increase of hormones as seen in IVF, but to date the data has been inconsistent.
The American Society of Reproductive Medicine has released an announcement this week highlighting a recently published a cohort study looking at more than 21,000 women in Western Australia over a 20 year period of time. The study, by Stewart et al., evaluated a group of women undergoing treatment for infertility, and compared rates of breast cancer in those who received IVF and those who did not. Women in the study who underwent IVF were on average older at the time of delivery of their first child and at their infertility diagnosis. Patients with a personal breast cancer history or who developed breast cancer within six months were excluded. The study found that women overall did not have an increased likelihood of breast cancer, but women who were younger at the start of their infertility treatment did in fact have a higher incidence of breast cancer. Women who first underwent IVF at age 24 were 1.5 times as likely to develop breast cancer than women who received a non-IVF infertility treatment at age 24. Women who began IVF at age 40 had no increased risk of breast cancer compared to women who began non-IVF treatment at 40. While delivery of multiples was associated with lower cancer rates, age at first delivery was associated with an increased breast cancer rate in both women who undergo IVF and women who do not.
The data was adjusted for confounders but did not specifically look at what types of hormone treatments were received by members of each group. As such, it is unclear whether these findings are directly related to the increased short-term exposure to estrogens. More research is needed to study the potential risk in young women, but for now women in their thirties and forties who are considering IVF should be reassured that increased rates of breast cancer did not appear to be associated with IVF treatment.
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