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IVF doesn't increase breast cancer risk -

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Norman Swan: For many years now there's been fears and conflicting evidence that in vitro fertilisation might increase the risk of breast cancer in women undergoing the procedure. A large 20-year study has come up with what many hope are definitive answers. One of the authors of the study is Alexandra van den Belt-Dusebout, and she is in the Department of Epidemiology at the Netherlands Cancer Institute, and she joins me on the line from Holland. Welcome to the Health Report, Alexandra.

Alexandra van den Belt-Dusebout: Hello, good morning.

Norman Swan: Why might IVF cause breast cancer?

Alexandra van den Belt-Dusebout: Female sex hormone levels increase during in vitro fertilisation, during the ovarian stimulation that is necessary for retrieving eggs, and sex hormone levels have been known to increase the risk of breast cancer.

Norman Swan: So you're not using oestrogen to stimulate the ovaries but they use hormones that stimulate the ovaries and then the ovaries produce oestrogen and then that drives the breasts, that's the theory.

Alexandra van den Belt-Dusebout: Yes, exactly.

Norman Swan: And what evidence before your study was there that there might be a risk?

Alexandra van den Belt-Dusebout: There had been many studies but the drawback was that the studies were limited in numbers of breast cancer, and the follow-up was too short to be sure what would be the risk in the long term.

Norman Swan: But it's not just increased hormone levels. When you do IVF you also decrease the hormone levels, don't you, to actually take control of the menstrual cycle.

Alexandra van den Belt-Dusebout: Yes, that's true. First the cycle…first the levels are decreased, and after that the ovarian stimulation takes place and the levels increase.

Norman Swan: So what did you do in this study?

Alexandra van den Belt-Dusebout: We had 25,000 women that had been treated for fertility problems: 19,000 IVF-treated women in the period 1983 to 1995, and also 6,000 women who received other fertility treatments in roughly the same period…

Norman Swan: So you were comparing IVF but you're also comparing women with infertility per se to see whether infertility itself had an influence on breast cancer.

Alexandra van den Belt-Dusebout: Yes, exactly. We followed all these women through December 2013, there was a median follow-up of 21 years, and we compared both groups with the general population in the Netherlands, and we compared the IVF group with the non-IVF group.

Norman Swan: And what did you find?

Alexandra van den Belt-Dusebout: We found that the risk was not increased, neither compared to the general population or with the non-IVF group, not even when the follow-up was more than 20 years. And there was also not a difference for the different types of treatment or different types of fertility diagnosis.

Norman Swan: On reading your paper, it looked as though the more IVF cycles, and you don't want women to have unnecessary IVF cycles, but the more IVF cycles a woman had, the less likely she was to develop breast cancer. What is going on there?

Alexandra van den Belt-Dusebout: Yes. Women who received more than six cycles of IVF and also women who had a low egg yield at the first IVF cycle had a decreased risk, and that can be explained because those women tend to reach menopause at an earlier age and an earlier age of menopause protects or decreases the risk of breast cancer.

Norman Swan: Which is also a story about oestrogen stimulation because the more menstrual cycles you have, the more oestrogen stimulation you have and therefore later onset of menstruation in your life and earlier cessation of menstruation decreases the risk of breast cancer. So that was nothing to do with IVF, that was simply a phenomenon of those women who were reaching the end of their fertile life a bit earlier than you might have expected.

Alexandra van den Belt-Dusebout: Yes, exactly. And that was exactly the reason, probably the reason that they had to go for IVF to still have a pregnancy.

Norman Swan: Ovarian stimulation isn't quite so aggressive these days, but presumably that's not the reason, it's presumably to improve outcome, so although these studies are not cause and effect, they are associations because you are just looking at the relationship between factors over time, can you be confident in saying to women now, look, it really doesn't look like breast cancer is a risk of IVF?

Alexandra van den Belt-Dusebout: Yes, these results are quite reassuring for women who have been treated with IVF in the past, and since the treatments have been quite similar in the different western countries we also have confidence that the results are applicable to other Western countries.

Norman Swan: What about other female cancers such as cancer of the uterus, endometrial cancer or ovarian cancer?

Alexandra van den Belt-Dusebout: In our study we are also looking into the risks of other hormone related cancers, and we recently did analysis on melanoma and colorectal cancer, and we didn't find increased risks either. We are also in the future investigating the risks of endometrial cancer and ovarian cancer and we will do that in an even larger cohort because we recently also included women who have been treated in the period 1995 to 2000. So then we have more than 40,000 women in the cohort.

Norman Swan: And we'll just follow that up and hopefully speak to you when you've got some results there before we set any panic afoot. Thank you very much for joining us, Alexandra.

Alexandra van den Belt-Dusebout: Okay, thank you.

Norman Swan: Alexandra van den Belt-Dusebout who is in the Department of Epidemiology at the Netherlands Cancer Institute. And as I say, you're listening to the Health Report here on Radio National, CBC Radio and ABC News Radio.


Guests
Dr Alexandra van den Belt-DuseboutDepartment of Epidemiology, Netherlands Cancer Institute

Further Information
Ovarian Stimulation for In Vitro Fertilization and Long-term Risk of Breast Cancer [$]

Credits
PresenterDr Norman Swan ProducerJoel Werner