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Abortion and breast cancer risk for Australian women

To the Editor: Recent comments in the media have renewed attention on the question of whether abortion is a risk factor for breast cancer, despite broad acceptance internationally in the scientific, medical and cancer advocacy communities that there is no association.

It was demonstrated in 2004 that abortion is not a risk factor for breast cancer, based on a combined analysis of prospective cohort study data from around the world.1 The authors showed empirically that retrospective case–control studies tend to give biased findings, most likely because women with breast cancer (cases) are more likely than controls to report previous abortions. Prospective cohort studies avoid this bias because information on abortions is collected before any of the women develop the disease. Indeed, a recent meta-analysis of findings from studies of Chinese women reported an apparent increased breast cancer risk associated with abortion based on case–control studies, but no evidence of association based on prospective cohort studies.2 Several other large prospective cohort studies have published consistently null results since 2004.3,4

In 1990–1994, the Melbourne Collaborative Cohort Study5 recruited 24 018 Victorian…