Review: spontaneous or induced abortion is not associated with development of breast cancer

摘要

The idea that breast cancer risk is increased among women who have had abortions is an important scientific theory that has been sensationalised by both pro-abortion and anti-abortion activists, who are willing to use a very mixed body of evidence for their own purposes.There are plausible biological mechanisms that might explain a relation between both spontaneous and induced abortions and the development of breast cancer. Regardless of the political context, it is important to understand the causes of this disease that might be amenable to behavioural change or public policy initiatives. However, this area of research has been plagued by methodological problems, including the problem of asking women to report induced abortions that may have occurred at a time when such procedures were illegal. Even very small differences in reporting between women with and without breast cancer could have led to the modest increases in risk reported in several studies.The reanalysis of data from 53 studies of abortion and breast cancer by the Collaborative Group on Hormonal Factors in Breast Cancer gets around many of the methodological shortcomings of earlier studies and meta-analyses by focusing on countries with liberal abortion laws and providing a separate analysis of 13 studies where information on abortions was recorded prospectively. This subgroup of studies included data on 44 000 women and found no effect of either spontaneous or induced abortion on breast cancer risk. This is strong evidence that no causal relation exists of either clinical or public health significance. Interestingly, although the prospective studies showed no effect of induced abortions on breast cancer, the reanalysed data from 39 retrospective studies showed a slightly increased risk-evidence of a systematic recall bias in these studies.Clinically, this study suggests that women who experience spontaneous abortion and women who are considering induced abortion can be reassured that no sound medical evidence exists that they will be at increased risk of developing breast cancer. With the publication of this methodologically sound and comprehensive reanalysis, it is hoped that resources available for breast cancer research can be redirected towards more fruitful lines of research into preventable causes.