Abortion and Breast Cancer Answers to Common Questions
by Joel Brind, PhD
Joel Brind is a Professor of Biology and Endocrinology at Baruch College of the City University of New York, where he has been teaching since 1986. His research on the connections between reproductive hormones and human disease has included breast cancer since 1982. His peer-reviewed research paper on the subject, "Induced Abortion as an Independent Risk Factor for Breast Cancer: A Comprehensive Review and Meta-Analysis," which he wrote in collaboration with colleagues at the Penn State College of Medicine in Hershey, Pennsylvania, appeared in the October 1996 issue of the Journal of Epidemiology and Community Health, published by the British Medical Association.
The data demonstrating a link between induced abortion and an increased risk of breast cancer grows more convincing every year. Those who cannot, or will not, face facts have only a few broad generalized criticisms on which to fall back. The following will equip you to answer those who deny that when women deliberately abort, they increase the likelihood they will suffer from breast cancer.
Regardless of what pro-lifers may say, hasn't there been more than 50 studies on the subject and isn't the abortion-breast cancer (ABC) link still inconclusive?
This is true only if you confuse and combine categories. For instance, if you include spontaneous abortion (miscarriage), then the results of the over 50 studies that have been published show no definite trend of increased risk of breast cancer. But if you (properly) define "abortion" as induced abortion (i.e., the matter of "choice"), the link is clear. Did you know that only 23 of these studies broke out spontaneous abortions versus induced abortions? Eighteen of the 23 show increased risk of breast cancer among women who've had any induced abortions. Only one of the 23 is inconsistent with an increased risk.
But your own argument works against you. Why shouldn't spontaneous abortion also increase the risk? After all, why should it make any difference how an uncompleted pregnancy is terminated if there is a connection?
Because the difference is in whether the pregnancy itself is normal. Normal pregnancies do not normally abort spontaneously. Many spontaneous abortions occur because the woman's ovaries secrete an inadequate amount of the pregnancy hormone progesterone. By contrast, secretion of progesterone is very high in a normal pregnancy, accompanied by high levels of secretion of estrogen (which is made from progesterone) by the ovaries.
Estrogen makes the breast tissue grow - - including any abnormal and potentially cancerous tissue. If the pregnancy is completed, other hormones act to cause the breast cells to differentiate into milk-producing tissue, or to die off if they're not needed. Differentiated cells are less likely to become cancerous. That's why a complete pregnancy tends to lower breast cancer risk.
However, if the pregnancy isn't completed, no late-term hormones kick in to differentiate the breast cells. Instead, the excess estrogen leaves the tissue in the growth-prone mode, free to grow into abnormal or even cancerous cells. Thus, more abnormal cells are left behind, and also more normal but primitive cells, which may become abnormal later on. That's why interrupting a normal pregnancy tends to increase breast cancer risk.
But to return to miscarriage, with most pregnancies that abort spontaneously, high estrogen levels are never generated in the first place. Thus, one would not expect an increased breast cancer risk because the "mechanism" is missing.
Even if it's conceded that the ABC link is real, the elevated risk is a very small one.
Epidemiologists call a risk factor "strong" if it is associated with an increase of at least several-fold (several hundred percent). For example, if a disease occurs in one in 100,000 women and a relatively weak risk factor raises the incidence 100 percent (up to one in 50,000), it would still be a very rare disease. However, the incidence of breast cancer in women in the United States now exceeds one in ten. Thus, because there are so many cases of breast cancer, even a barely detectable increase in risk would result in a considerable increase in the number of women with breast cancer.
There is an additional dimension to this question which has to do with frequency of exposure. Suppose the risk of even a common disease such as breast cancer would be greatly increased if a woman traveled in space. Obviously, the "exposure" would be next to nothing as there are not many women who've circled the globe in a space shuttle.
By contrast, with induced abortion, there is a huge exposure: 1,500,000 abortions each year, about 800,000 are to women having their first abortion. Even a relatively small increased risk of 10 percent means thousands of new cases of breast cancer. To use numbers: 10 percent (the incidence of breast cancer in women) times 10 percent (the increased risk specifically due to having had an abortion, which even many of those skeptical of an ABC link seem willing to concede) times 800,000 (the number of first abortions each year) totals 8,000 more cases of breast cancer each year.
These numbers keep changing. The Boston Globe reported an increased breast cancer risk of 12 percent.
This is the figure the Globe pulled out of a January 1996 Journal of the American Medical Association article. It should be noted, however, that this figure was arrived at by mixing in spontaneous abortion, an often used but invalid maneuver at which we've already looked. The actual risk increase due to induced abortion reported in the JAMA study was 23 percent. But even this was likely an underestimate. If you put together all the studies that have been done since 1957, the overall average risk increase comes out closer to the 50 percent reported by Janet Daling, et al., in the Journal of the National Cancer Institute in November 1994.
This means some huge numbers. Specifically, we multiply 10 percent (the percentage of women who will contract breast cancer at some point in their lives) times 50 percent (the increased risk due to having an induced abortion) times 800,000 (the annual number of women having an abortion for the first time) equals 40,000 additional cases of breast cancer.
If that were true, there should be 40,000 excess cases of breast cancer a year in this country because of induced abortion. Are there?
Not yet. The average latency period for breast cancer, as for most other forms of cancer, is very long; between several years and several decades. So the number of additional breast cancer cases from induced abortion would not reach the 40,000 range until well into the 21st century, when the first group of women who reached reproductive maturity after Roe v. Wade reaches old age. Right now we are seeing 5,000 - 10,000 excess cases a year.
Will a projected risk increase of 50 percent hold up in terms of lifetime risk?
Since the legalization of abortion is still relatively recent, few studies are of women old enough to find out if the 50 percent relative risk still holds for them at older ages. Unfortunately, these few studies actually suggest that the risks grow even worse. A 1993 Howard University study examined a population of African-American women, most of whom were age 50 and over. There was indeed a 50 percent risk increase among women 40 and under. But the risk increase was 180 percent for women in their 40s, and a whopping 370 percent for the 50-and-over group.
Intriguingly, the recent JAMA study actually showed a similar trend. The risk increase rose steadily from about 10 percent for women in their 40s and younger, up to over 100 percent for women 70 and over.
Virtually everyone agrees that when a woman has her first child at an early age, it lowers her chances of having breast cancer. So, isn't the apparent ABC link simply due to the fact that abortion is one way the first childbirth is delayed?
No. Most of the epidemiological studies already subtract out the effect of delayed first childbirth. But this question raises another important point: A teenager or younger woman who aborts her first pregnancy is increasing her breast cancer risk in two ways. Because of the natural protection against breast cancer from an early full-term pregnancy, a pregnant 16-year-old who carries the child to term will reduce her lifetime risk from about 10 percent to about 7 percent. This is not a matter of controversy; completed early first pregnancies reduce breast cancer risk. But if she has an abortion, she apparently increases her lifetime risk by at least 50 percent (from 10 percent to about 15 percent). Thus, the net total effect of the abortion might be to double her breast cancer risk over what it would be if she had carried the child to term - - loss of protection, plus increase in risk.
What do you mean by "might be?"
It might be a lot worse. For example, one disturbing finding of the 1994 Daling study was that for women who had had an abortion before age 18, the risk went up 150 percent. (Teenagers currently make up 21 percent of abortion patients.) But even more ominous was its finding that for women who had an abortion before age 18 and who had a family history of breast cancer, the risk was incalculably high. All 12 women in the study with such a history ended up with breast cancer by the age of 45.
Even so, you have to grant that the overall average breast cancer risk increase with abortion is still small compared to a really strong link such as that between cigarette smoking and lung cancer.
That's really about individual exposure to a given risk factor. Yes, you do see a tenfold increase in lung cancer risk with smoking, if you smoke a pack a day for ten years. But then again, that's 73,000 cigarettes! One cigarette doesn't give anyone lung cancer. And even with thousands of cigarettes, the risk can be reversed if you quit early enough. On the other hand, one "exposure" -- one choice to have an abortion -- measurably increases breast cancer risk. And abortions are not reversible.