For many years there were conflicting reports about the emotionally charged topic of whether miscarriages (=spontaneous abortions) or induced abortions (also simply known as abortions) would lead to an increased risk for these women later in life. The problem was that the studies could not be directly compared because they differed in size, in age group and whether the women had one or more children or none.
The studies also differed in respect to whether they were prospective or restrospective. In this context a prospective study is one where it was known at the outset before the women developed breast cancer whether or not there was a history of a spontaneous or induced abortion in the past. A retrospective study would be one where a group of women with established breast cancer would be asked retrospectively whether or not they had a history of abortions (spontaneous or induced).
It turns out that the discrepancies between these studies in the past were largely because of the significant difference between the data of the unreliable retrospective studies and the very reliable prospective studies.
On March 27, 2004 the Lancet reported about a study that had been undertaken by the Collaborative Group on Hormonal Factors in Breast Cancer (seat of the Secretariat in Oxford, England). This study involved hundreds of scientists and clinicians from the major Cancer Clinics around the world who gathered the world-wide epidemiological evidence about breast cancer and pooled the data regarding 53 studies from 16 countries.
A total of 83,000 women with breast cancer around the world had been included in this study. The data was separated into sub-categories. For instance, 44,000 women were included in the prospective branch of the study and 33,000 in the retrospective branch. The data was carefully controlled for the factors mentioned above and many other differences to ensure that the data could be compared (rules of evidence-based medicine).
The surprise finding was that there was no statistical difference regarding the risk for developing breast cancer in the prospective branch of the study between the group of women who never were pregnant, those who had one or more children and those who had miscarriages or abortions in the past. However, the retrospective studies reported a higher incidence of breast cancer because of an observer bias. The researchers and clinicians concluded that the data of the restrospective studies were unreliable because they were not carefully controlled and there likely was more reliable reporting of the women who had developed breast cancer than the control groups who likely underreported their histories thus resulting in misleading conclusions.
Summary: Women do not have a higher risk of developing breast cancer following spontaneous or induced abortions. Forget all of the fear-mongering that you may have heard in the past in the popular press.
More information about causes of breast cancer: http://nethealthbook.com/cancer-overview/breast-cancer/causes-breast-cancer/
Lancet 2004; 363: 1007-16.
Last edited October 26, 2014