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Study Dispels Abortion-Breast Cancer Link

Findings Show Abortion Doesn't Raise Breast Cancer Risk

WebMD Health News

March 25, 2004 -- A major new study on the relationship between abortion and breast cancer suggests that pregnancies ending in abortion do not increase a woman's risk of developing breast cancer.

British researchers reviewed studies involving 83,000 women and found that pregnancies ending in abortion or miscarriage (also known as spontaneous abortion) do not significantly affect a woman's risk of developing breast cancer.

"This is the first time that the vast majority -- over 90% of studies that have ever looked at the relationship between abortion and breast cancer -- have been brought together and looked at," says researcher Valerie Beral, professor of epidemiology at the University of Oxford, England. "Overall, we found quite clear evidence that there's no increased risk of breast cancer from either miscarriage or abortion."

Researchers say previous studies that suggested having an abortion slightly increases a woman's risk of breast cancer were flawed because they were based on women reporting having had an abortion after a diagnosis of breast cancer, known as a retrospective study.

"Studies can give misleading results if women are asked about previous abortions only after they are diagnosed with breast cancer," says researcher Richard Peto of Collaborative Group on Hormonal Factors in Breast Cancer, in a news release. "This may well be because, on average, women with breast cancer are more likely than other women to disclose any prior induced abortions."

Therefore, their analysis relied primarily on studies based on information on abortion collected before the diagnosis of breast cancer, known as a prospective data.

Despite the results of this study, which agree with several recent consensus statements from major medical organizations, the controversy surrounding the issue isn't likely to falter due to the highly political nature of the abortion debate.

Sorting Through the Studies on Breast Cancer and Abortion

In the study, published in the March 27 issue of The Lancet, researchers analyzed data on individual women from 53 studies in 16 countries. Researchers compared the effects of having an abortion or miscarriage with those of never having been pregnant on breast cancer risk.

The study was funded by Cancer Research UK.

According to data from 44,000 women who participated in the studies analyzed, researchers found no increase in breast cancer risk among women who had a pregnancy that ended in miscarriage or abortion. In fact, women who had a pregnancy that ended in abortion had a slightly lower (7%) risk of breast cancer, and the number of abortions was not associated with any change in breast cancer risk.

"You could argue that if anything there is a small decreased risk, but I think the main thing is that it confirms very strongly that we can say quite confidently that there is no increased risk," says Beral.

Beral says the data collected from the 39,000 women who participated in retrospective studies were less reliable. Although the links between breast cancer and miscarriage were similar among the retrospective and prospective studies, the results on abortion and breast cancer varied widely between the two types of studies.

"If you've got something we know is correct, and something we're not sure about," says Bernal referring to the studies that look at data collection prospectively and retrospectively, "and we get a one-in-a-million chance that these results are similar, it suggests that the other ones are biased."

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