No Breast Cancer Risk from IVF Treatment Hormones

No Breast Cancer Risk from IVF Treatment Hormones
These human embryos are fertilized and ready to be implanted in a woman's womb in an IVF procedure. Photo courtesy Microscopy.

Fertility treatments, including in vitro fertilization (IVF), can cause hormone levels to fluctuate wildly. Although some have worried these hormones could increase the risk of breast cancer, a new study has put those fears to rest.

The study comes from Alexandra W. van den Belt-Dusebout and other researchers at the Netherlands Cancer Institute in Amsterdam. The researchers published their results in the July 19th issue of the Journal of the American Medical Association (JAMA). By analyzing the incidence of breast cancer in women who either had or did not have IVF treatments, the researchers hoped to determine once and for all if fertility treatments increase the risk.

IVF treatments involve taking fertility drugs to stimulate the ovaries, producing more eggs. These eggs are then available to be removed, fertilized, and re-implanted in the patient. Doctors use a variety of different drugs to stimulate the ovaries, but often they are either made of hormones or other compounds that will increase or decrease hormone levels, triggering the ovaries to release eggs.

The researchers studied two groups of women, with 19,158 women starting IVF treatment between 1983 and 1995, and 5,950 women starting other types of fertility treatments between 1980 and 1995. At the beginning, the average age of the women was 33, and of the women who underwent IVF treatment, the average number of IVF cycles was 3.6.

Over the next 21 years or so, there were 948 cases of breast cancer in both the IVF and non-IVF groups combined. About 3 percent of the IVF group developed breast cancer, while 2.9 percent of the non-IVF group developed breast cancer within the next couple of decades. The risk of breast cancer also did not seem to differ between types of fertility drugs the women received. Since there was not a significant difference in risk of breast cancer between the IVF and non-IVF groups, there seems to be no increased risk of breast cancer with IVF treatments.

The researchers did find, interestingly, that women who had seven or more IVF cycles seemed to have a decreased risk of breast cancer compared to women who underwent only one or two IVF cycles. That finding could be interesting for future studies to examine. The researchers emphasize that more research should take a closer look at the relationship between IVF drugs and breast cancer risk, but the current study is helpful for women considering IVF. If they were worried that these fertility treatments would increase their risk of breast cancer, these women can put their minds at ease about choosing IFV.

Breast cancer is common, and increasing numbers of women are opting for ovarian stimulation and IVF treatments, so if IVF treatments increase breast cancer risk it would be a public health problem. Previous research has suggested that the hormones estrogen and progesterone can affect breast cancer risk, and IVF treatment drugs affect these and other hormones. However, the researchers in the current study speculate that because IVF treatments usually last only about a couple of weeks for each cycle, the drop in estrogen and progesterone levels may be too short to have an effect on breast cancer development.

IVF doctors use ovarian stimulation to temporarily increase the number of mature eggs a woman produces. The more eggs they retrieve from the patient, the higher chance they can select a quality egg for fertilization. Doctors may use injections of follicle-stimulating hormone to achieve this, directly giving a woman an increased level of this hormone which causes more eggs to form. These doctors may also prescribe other drugs, such as Clomid or Letrozole, to block certain hormones, thus allowing other hormones to trigger egg production.

The hormones estrogen and progesterone affect different aspects of a woman’s body, including prompting breast cells to develop. However, when a woman’s estrogen levels increase, researchers believe this can increase the growth of breast cancer. Estrogen levels can vary naturally or can rise with the use of oral contraceptives, menopause treatments, and other drugs. Too much estrogen over a lifetime could increase the risk of breast cancer, so doctors usually try to limit the length of time women are taking hormone replacement therapy for menopausal symptoms.

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