Cancer–abortion link quashed

NEW Australian research has again ruled out any link between abortion and breast cancer, after experts were prompted to review local data in response to suggestions in the media that such a link may exist.

In a research letter published by the MJA, Victorian cancer researchers detailed a prospective cohort study in which they found no association between abortion in the first trimester and breast cancer. (1)
    
Similarly, no breast cancer link was found with abortion before first full-time pregnancy or with abortion in the first two trimesters.

The researchers reviewed the records of 24 018 Victorian women, aged 40‒69 years who were free of cancer when their data were collected between 1990 and 1994 as part of the Melbourne Collaborative Cohort Study. (2)

These records, which included information on all pregnancies but did not differentiate between spontaneous and induced abortion, were reviewed against the Victorian Cancer Registry. The researchers found that up to December 2012, 1235 of the women were subsequently diagnosed with breast cancer.

The findings came after media reports that senior federal government minister, Senator Eric Abetz, had suggested on a commercial news program that there was a link between abortion and breast cancer, sparking condemnation by medical experts. Senator Abetz later denied making such a claim. (3)

Professor Kelly-Anne Phillips, a coauthor of the MJA research letter and head of the Breast and Ovarian Cancer Risk Management Clinic at the Peter MacCallum Cancer Centre, said the recent controversy was surprising, particularly given that such a link had been ruled out by an analysis of data from 53 studies a decade ago. (4)

“We, along with many national and international organisations, including Cancer Australia, had been very clear that there is no link, based on the previous, pretty vast literature that was out there”, Professor Phillips told MJA InSight.

However, she said that until now the only Australian data available was a case–control study from the 1980s which purported to show a link between breast cancer and abortion. She said there was good literature demonstrating that reporting bias was present in case–control studies of this issue, so they tended to erroneously show a link.

“We decided it was important to look at this question prospectively in an Australian cohort”, she said.

“It’s a prospective study, it’s much more robust and, as with the other prospective studies internationally, we did not show a link between abortion and breast cancer. That’s clear.”

Associate Professor Stephen Robson, vice-president of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG), said the idea that termination of pregnancy (TOP) might cause breast cancer had been suggested as a hypothesis about 35 years ago, based on small-scale animal experiments.

“However, thorough and extensive analysis of data in the subsequent years has not unearthed any causative link between TOP and breast cancer. Any correlation between the two is likely to represent a bias due to recall — women who have breast cancer are more likely to think about events in the past and are more likely to tell investigators about a previous TOP than women who do not have breast cancer”, he said.

“RANZCOG, like virtually every women’s health body around the world, does not support any link between TOP and subsequent breast cancer.”

Cancer Australia also confirmed that the research on this issue is clear. “Research has shown there is no link between termination of pregnancy and increased risk of breast cancer. This includes both induced abortion and spontaneous miscarriage”, a Cancer Australia spokesperson said.

Ms Katie Clift, a spokesperson for Cancer Council Queensland, told MJA InSight: “This local research is important, and reinforces the latest evidence, which should well and truly put this issue to rest.”

1. MJA 2014; Online 29 September
2. Cancer Council Victoria: Overview of Melbourne Collaborative Cohort Study
3. Senator Eric Abetz: Statement regarding incorrect reports, 8 August 2014
4. Lancet 2004; 363: 1007-1016 http

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