Cool heads needed on the abortion-breast cancer link

A Mexican wave of moral indignation swept through the chattering class this month when the hypothesis was raised of a link between abortion and breast cancer.  We heard, in shrill tones, that claims of such a link are “factually incorrect” (blogger Mia Freedman), “absurd” (Simon Breheny of the IPA) and even “an insult to all women” (Greens MP Adam Bandt). With the arrival this week of breast surgeon and cancer researcher Dr Angela Lanfranchi to speak to this hypothesis, we can expect a resurgence of this rage.

Yet no such public frenzy occurred when the closest male equivalent – a correlation between vasectomy and prostate cancer – was proposed only last month. Why is it a slur against women to consider a link between abortion and breast cancer, but no slur against men to suggest that vasectomy might be linked to prostate cancer? Both hypotheses remain unproven, plagued by conflicting evidence, yet both deal with grave medical issues that demand ongoing dispassionate research.

Consider last month’s publication on prostate cancer in the Journal of Clinical Oncology. It was a 24 year follow-up study and concluded, “Our data support the hypothesis that vasectomy is associated with a modest increased incidence of lethal prostate cancer”. Yet look back over that 24 year period and you will see that the vasectomy-prostate cancer hypothesis has waxed and waned, just like the abortion-breast cancer hypothesis.

In 1993 the Journal of the American Medical Associationinvestigated the question, “Vasectomy and prostate cancer: chance, bias, or a causal relationship?” and made the point that “any causal relationship between the two would be important both for individual and public health”. The same point should be calmly made about any relationship between abortion and breast cancer. A decade later, the ABC’s Health Report commentator Dr Norman Swan exulted in newer prostate research published in the same prestigious journal, telling his male listeners, “There has been some concern about an alleged increased risk of prostate cancer after vasectomy. But recent research from New Zealand found no link between them - so the only excuse now is cowardice!”

Contrast the good-natured commentary on the prostate cancer theory to the vulgar chorus of denunciation of the breast cancer theory.

Yet if the link between abortion and breast cancer is not worthy of consideration, why does the question keep being raised in peer-reviewed medical journals? When four of the five largest studies on this subject in the past two years report a significant correlation, why did medical authorities stand by this month and let this inoffensive hypothesis be lynched by an ignorant mob? Worse, why did the President of the AMA, Dr Brian Owler, do such injustice to the published research with his categorical statement, “There is no evidence to say breast cancer and abortion are linked. Let’s not use false evidence or try and link abortion with other things such as breast cancer.”

The truth is far more interesting, and concerning, than Dr Owler’s dismissive sound bite. Pause and consider just three major studies from the last three years.

In February this year in the journal Cancer Causes & Control, Huang et al published “A meta-analysis of the association between induced abortion and breast cancer risk among Chinese females”. After analysis of 36 studies covering 14 provinces in China the authors concluded, “Induced abortion is significantly associated with an increased risk of breast cancer among Chinese females, and the risk of breast cancer increases as the number of induced abortions increases.” 

By contrast, last year a large Danish study investigated “Induced abortion and breast cancer among parous women” and concluded, “Our study did not show evidence of an association between induced abortion and breast cancer risk.” (Brauner et al, in Acta O&G Scandinavica) 

In the journal Breast Cancer Researchin 2012, Lecarpentier et al investigated “Variation in breast cancer risk associated with factors related to pregnancies” in the cohort of French women who carry the breast cancer genes BRCA 1 and 2. They concluded: “We found an increased breast cancer risk associated with an increasing number of induced abortions.”

Take a closer look at the Lecarpentier paper, which was a model of sober caution and acknowledged the contentious nature of this topic: “A number of studies have examined the risk of breast cancer associated with interrupted pregnancies, but there has been some controversy in the past.”

After reviewing some studies with negative findings they state, “However, numerous studies have suggested that interrupted pregnancies may moderately increase the risk of breast cancer”.