Higher Breast Density Found in Women Who Received Hormonal Fertility Treatment

Women with a history of infertility, and have undergone hormonal fertility treatment have denser breast tissue, which may increase their risk of developing breast cancer, according to a study published in the journal Breast Cancer Research.

Frida Lundberg

Women with a history of infertility, and have undergone hormonal fertility treatment have denser breast tissue, which may increase their risk of developing breast cancer, according to a study published in the journal Breast Cancer Research.

Researchers with the Karolinska Institutet in Sweden discovered this after conducting a 3-year study of 43,313 women, aged 40 to 69 as part of the KARolinska MAmmography (KARMA) project for risk prediction of breast cancer.

Of those women, 8963 reported fertility problems and 1576 had undergone controlled ovarian stimulation (COS) or a hormone treatment required for in vitro fertilization. Another 1429 had hormonal stimulation without COS, and 5958 had not received any hormonal fertility treatment.

COS is a hormone replacement therapy that increases estrogen and progesterone levels. It has been suspected of increasing a patient’s risk in developing breast cancer.

Breast density can also play a role in increased breast cancer risk. Previous studies have indicated that women who have extremely dense breasts are at least 4 to 6 times more likely to develop breast cancer than women with nondense, fatty tissue breasts.

Hormone replacement therapy, like COS, increases estrogen and progesterone levels and has been suspected to increase breast cancer risk. This is the first population-based study to investigate the effect of infertility and hormone stimulation on mammographic density which may be a useful marker for the effect of hormonal fertility treatment on breast cancer risk, especially in women below the age at which breast cancer is normally diagnosed (≥50 years).

The authors of the study stated that women with a history of infertility had a 1.53 cm higher absolute dense volume compared to noninfertile women. Among the group of infertile women, those who had gone through COS treatment had higher absolute dense volume compared with those who decided not to receive hormone therapy.

"The results from our study indicate that infertile women, especially those who undergo COS, might represent a group with an increased breast cancer risk,” Frida Lundberg, lead author of the study, said in a statement. “While we believe it is important to continue monitoring these women, the observed difference in breast tissue volume is relatively small and has only been linked to a modest increase in breast cancer risk in previous studies."

The researchers cautioned that due to the cross-sectional design of the study, which assessed history of infertility and breast density at the same time, no causal links between hormonal fertility treatment, infertility, and breast density could be established; however, the research team advised that continued monitoring of women undergoing COS is warranted.

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Lundberg FE, Johansson AL, Rodriguez-Wallberg K, et al. Association of infertility and fertility treatment with mammographic density in a large screening-based cohort of women: a cross-sectional study. Breast Cancer Res. 2016;18(1):36.