Abortion and Breast Cancer: A Conversation

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I recently had an interesting e-mail conversation about the connection between abortion and breast cancer with someone who takes issue with some of the statements we have made on the subject. While her tone was, as you shall see, rather belligerant, she nevertheless brought up a couple of important points that, I thought, deserved an answer. As others may have similar questions, we thought it might be useful to post excerpts of this conversation.

Her original e-mail said:

Anti-Abortionist[s] will stop at nothing to try and stop abortions, even misinformation and there is plenty. There are not that many breast cancer patients that have even had an abortion. What would the same research show if they would have had had their gall bladders or appendix out instead of an abortion. ... Stop your crap!!
About 180,000 women are diagnosed with breast cancer each year. Extrapolating from the statistics that cancer researcher Dr Janet Daling collected, it appears that of these, about 80,000 had an abortion at some time in their lives prior to the diagnosis. This surely qualifies as "many".

What the writer appears to be saying with the gall bladder / appendix statement is that if you chose any group of women at random, some of them would get breast cancer, and so the fact that some had abortions doesn't prove that abortion causes breast cancer. But this misses how studies like this are done. I'm not aware of any studies that investigated a connection between having one's gall bladder or appendix removed and getting breast cancer. If, as I would guess, these have nothing to do with breast cancer, then one would expect to find that the percentage of women who had gall bladders removed and later got breast cancer would be just about the same as the percentage of women who did not have gall bladders removed and later got breast cancer. If, say, 5% of all women get breast cancer, then we would expect that 5% of the women who have had their gall bladders removed will get breast cancer. That is, having a gall bladder removed would have no effect on the chance that you get breast cancer. If in fact we found that 10% or 15% got breast cancer, than we would have reason to conclude that removing a gall bladder does cause cancer. What most studies on abortion and breast cancer have found is that women who have had abortions are about 50% more likely to contract breast cancer as women who have not had abortions. One researcher, Dr Joel Brind, found 30 studies that have been done on the subject, of which 24 found a statistically significant connection, and 6 did not.

If you are pro-choice, then surely you want women to make informed choices. Personally, I believe that people should have the legal right to smoke if that is what they want to do. But that belief does not lead me to say that any evidence linking cigarette smoking to long cancer should be ignored or suppressed, or to accuse people who bring up such evidence as zealots trying to take away smoker's rights. I think people considering whether to smoke should have all the information on the subject available to them.

Her next email was more thoughtful.

Scientists are trying to learn whether having a miscarriage or an abortion increases the risk of breast cancer. Thus far, studies have produced conflicting results, and this question is still unresolved. ... [A]nother thing I'm not seeing in all these studies is the complete reproductive history of the women involved. ...

Other factors, such as age of first menses, age at menopause, HRT, family history of breast cancer, etc. etc. and the overall picture is pretty muddy. And on top of that, there's still several factors you're not taking into account that have surely contributed to the rise in breast cancer incidence, such as ... increased obesity ... consumption of processed foods ... [and] environmental pollution. ...

How would you like it if I did a study on men and prostrate cancer and the study showed a small link between men that had sex with ladies of the night and I continually plastered it over the web, got on tv shows, and worked feverishly like you pro-life and anti-abortion people do to see how many people I could get to believe it so they would stop having sex with whores. Same difference!!

It is true that studies have produced conflicting results, but, as I noted earlier, the overwhelming majority of studies have found a statistically significant correlation. The fact that some studies have not found a connection is certainly a valid reason to say that a connection is not "proven", and the increased risk found -- generally on the order of 50% -- is less than what medical researchers commonly consider a sufficient increase to call "proof". But the evidence at this point is surely strong enough to say that there is cause for concern. Products have been banned from the marketplace on less evidence.

Regarding the other possible risk factors that she mentions, the point of the studies in question is to see if there is a connection between abortion and breast cancer, not age of first menses or whatever and breast cancer. Those are certainly valid and interesting things to investigate, but you can't investigate everything in one study. In general when one does a study such as this, you try to get a large enough sample that any other factors that might affect the outcome will tend to average or cancel out. If you could present an argument that some other risk factor for breast cancer is somehow associated with abortion, then this would be a valid criticism of these studies. For example, if you could show that women who are overweight are at higher risk for breast cancer, and that women who have had abortions are more likely to be overweight, then you could conclude that perhaps it was not the abortion that caused the breast cancer but rather being overweight. Of course I just made that example up for illustration, it sounds pretty unlikely, but perhaps you could find a more plausible scenario. But failing that, any other risk factors should be irrelevant. Sure, women who have a family history of breast cancer are more likely to get breast cancer themselves. But if roughly the same percentage of women who have had abortions as women who have not had abortions have family histories, then this factor would simply average out.

No one is claiming that abortion is the sole cause of breast cancer. Of course many women who have breast cancer have never had an abortion. No one claims that cigarette smoking is the sole cause of lung cancer. There are people who have lung cancer who have never smoked in their lives. This hardly proves that smoking is not an important risk factor.

Note that you could raise the sort of objections that she raises here against any study claiming to find risk factors for breast cancer, or any other disease for that matter. She lists a number of risk factors for breast cancer that she claims "muddy the waters". She apparently accepts studies that claim to have found such a link. Why does the writer -- not to mention numerous pro-abortion organizations -- find studies that link all these factors to increased risk of breast cancer convincing, but when exactly the same methods are used to investigate a link between abortion and breast cancer, suddenly the technique is fundamentally flawed and all results are suspect?

I'm baffled why she came up with the final prostate cancer / prostitution example. From her tone it appears that she assumes that we will be offended by this analogy, as if she just takes it for granted that we would be deeply upset by anything that might cast prostitution in a bad light. She thinks that people who oppose abortion are pro-prostitution? I don't get it.

Her final e-mail:

In closing ... We all know how abundant abortions have been in Asian countries for centuries and yet the breast cancer rate is five times higher in the US. ...

The pro-life and anti-abortionist will shamelessly inflate numbers, use flawed studies, and anything else to further their agenda. Killing people for your cause makes people despise you even more...

Actually the U.S. abortion rate is among the highest in the world, so if it is true that breast cancer rates here are higher than in Asia (I don't know if that's true -- I don't have statistics on it), that would hardly be an argument against an abortion / breast cancer connection. Of course there are so many differences in risk factors between here and there -- environment, diet, available medical care, etc, etc -- that assuming that all these factors would average out would be much more questionable. There's a big difference between comparing two groups of people who live amongst each other and have similar backgrounds except for one factor, and comparing two groups of people who differ in many ways.

The last statement is puzzling. How does it kill anyone to warn them of a possible danger, even if the warning proves premature? Suppose that researchers who have found a connection between abortion and breast cancer are wrong, and some number of women have decided not to have abortions based on warnings that proved unfounded. It's difficult to see how this could result in any of them dying. Surely the most that a pro-choice advocate could possibly argue is that this would cause them to unnecessarily suffer social and economic inconveniences brought on by an unwanted child. These warnings are not killing anyone. On the other hand, suppose that the researchers who have found this connection are right. Then "pro-choice" leaders who have fought warning women about this connection have kept secret from women a known danger. They are then indirectly responsible for some number of women getting breast cancer, a disease which can be fatal if not caught early. Who is it who is killing people to further their own agenda here?

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Posted 6 July 2002. Minor clean-up 16 Oct 2003.

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