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Fertility treatments may impact on breast cancer risk

Infertility and hormonal fertility treatments appear to increase density of breast tissue

Ingrid Torjesen

Wednesday, 13 April 2016

Infertility and hormonal fertility treatments may influence the amount of dense tissue in the breast, a risk factor for breast cancer, according to a study* published in the open access journal Breast Cancer Research.

Researchers at Karolinska Institutet, Sweden found that women with a history of infertility had denser breasts than other women and the association was more pronounced in women who had undergone controlled ovarian stimulation (COS), the hormone treatment required for in vitro fertilisation. While this may indicate a potential adverse effect of COS on breast density, the researchers point out that the effect may be due to the underlying infertility rather than to the treatment itself.

The researchers selected 43,313 women aged between 40 and 69 years who had mammograms as part of the KARolinska MAmmography project for risk prediction of breast cancer (KARMA) between 2010 and 2013. The women also responded to a questionnaire including questions about age, height, weight, smoking status, alcohol consumption, history of infertility, and family history of breast cancer. Out of 8,963 women who reported fertility problems, 1,576 had undergone COS, 1,429 had had hormonal stimulation without COS and 5,948 had received no fertility treatment.

The researchers first compared mammographic density levels between fertile and infertile women and then between infertile women who had never received hormonal fertility treatment to those who had.

Breast tissue is composed of two types of tissue: dense, fibroglandular and non-dense, fatty tissue. Women with extremely dense breasts have a four to six fold higher risk of developing breast cancer than women with non-dense breasts.

The researchers found that the women with a history of infertility had higher absolute dense volume - that is more dense, fibroglandular breast tissue - than non-infertile women. Among infertile women, those who had undergone COS had higher absolute dense volume than those who had not received any hormone treatment.

As this study relied on self-reported information and it was not possible to capture specific diagnoses from the existing KARMA data, the researchers warned that there may be a risk of misclassification of fertility and infertility and that the study also lacked information on the timing and number of treatment cycles each woman had gone through.

Whether differences in breast density may affect potential breast cancer risk in this population remains unknown, the authors said. Given the observed, moderate association between infertility, hormonal treatments and breast density, continued monitoring of women undergoing COS is warranted.

Frida Lundberg, lead author of the study, said: "The results from our study indicate that infertile women, especially those who undergo COS, might represent a group with an increased breast cancer risk. 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."

* Lundberg FE, 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 Research 201618:36. DOI: 10.1186/s13058-016-0693-5

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