Does Childbirth Cause Cancer?

There's no scientific debate on this one--women who give birth have an increased risk of breast cancer for the next fifteen years. Journals reporting this link include:

• New England Journal of Medicine (1994)
• American Journal of Epidemiology (2000)
• Cancer Causes Control (2002)

Why haven't you heard about this? First, because it's only temporary, and second, because the overall effect of childbirth is to reduce a women's lifetime risk. Young women have a very low risk of breast cancer, so a small increase in a very low risk is not a big problem. Older women have a much greater risk of breast cancer, so a long-term reduction in risk makes a big difference. That's why having children is generally associated with lower breast cancer risk.

 That's good news. But it leaves us with two questions. Why does breast cancer risk go up after childbirth? Why does it go down again after 15 years?

Jose and Irma Russo, of Fox Chase Cancer Center in Philadelphia, have done countless studies on the physiology of breast tissue. They have demonstrated that breast tissue specializes during the latter stages of pregnancy, leaving mature tissue at a lower risk of cancer. The early stages of pregnancy, by contrast, are a time of rapid cell division. (Women who have had babies know about this--tender breasts are one of the earliest signs of pregnancy.) These rapidly-replicating cells are a higher risk of mutation.

The prime suspect for the transient risk after childbirth is estrogen.  Estrogen helps prepare a woman's body for birth. It is the "gasoline" that keeps the human race going--but gasoline can be dangerous. All it takes is a spark to create an explosion. If you add enough estrogen to just one abnormal breast cell you can grow a tumor.

The good news is that the hormones of later pregnancy may actually stop some tumors in their tracks. The research to date is consistent with research on rats which indicates that tumors which have already begun to grow are redirected into normal tissue. (If you enjoyed biology in high school, read this article--it spells out the mechanism by which stem cells of one type are converted to another, and zeroes in on the precise tissue types that are at risk in early pregnancy.) If estrogen is the "gasoline" that catches fire, the hormones of later pregnancy are "rain" that puts fires out.

These are plausible answers to our two questions (why does risk go up after childbirth? Why does it go down after 15 years?), but if they turn out to be correct, they lead directly to a third question. What happens if a woman's breast cancer risk is raised by early pregnancy without the protective effect of later pregnancy? What if there's gasoline but no rain?

Research on rats proves that an interrupted pregnancy confers no protective effect. How about humans? If women have an elevated risk after any pregnancy (not just a full-term pregnancy), then women who choose abortions should have an elevated risk for at least 15 years after the procedure, just like other women who were pregnant. Carefully designed studies of breast cancer in young women find exactly that. Dr. Janet Daling, of Seattle's Fred Hutchinson Cancer Research Center, found:

Among women who had been pregnant at least once, the risk of breast cancer in those who had experienced an induced abortion was 50% higher than among other women (95% CI = 1.2-1.9). While this increased risk did not vary by the number of induced abortions or by the history of a completed pregnancy, it did vary according to the age at which the abortion occurred and the duration of that pregnancy. Highest risks were observed when the abortion was done at ages younger than 18 years—particularly if it took place after 8 weeks' gestation—or at 30 years of age or older. 

To answer the question posed by the title: childbirth does not cause cancer. Pregnancy does--in the sense that it adds "gasoline" that can burst into flame. Full-term pregnancy is the rain that puts fires out and reduces the risk of fire thereafter.

Chinese Abortions and American Health

In 1981, Dr. Malcolm Pike studied 163 Los Angeles breast cancer patients under the age of 33 and found that women who had used oral contraceptives were significantly more likely to get breast cancer than women who did not. The "relative risk" for women who had taken the Pill for six years of more was 2.2--which means they were twice as likely to get breast cancer as were women who did not take the Pill... with one exception. Women who had abortions (instead of relying on oral contraceptives) were even more likely to get breast cancer.

Pike did not zero in on abortions and the Pill because he disapproved of them on religious grounds, but because both of them expose a woman to estrogen. Estrogen has a well-documented impact on breast cancer risk. The Pill artificially adds estrogen to a woman from the outside, while pregnancy adds estrogen from the inside. Estrogen raises the risk of breast cancer in the 15 years after a normal birth, but the final stages of pregnancy mature the breast tissue so much that the overall effect of childbirth is to lower a woman's lifetime risk. Abortion leaves women with all the elevated risks of early pregnancy and none of the protective effects of third-trimester maturation.

The women in Pike's study were all under 32 when they got cancer. That's how many years have passed since Pike first published his findings. What has happened since then? Wikipedia lists 113 references on its "abortion/breast cancer hypothesis" page, and many of them show an elevated risk after abortion. The elevated risk is small, as these things go--a transient increase in risk of about 3% per week of terminated pregnancy. It takes a big study to turn something that small into a significant finding, and most of the big studies have been funded by big organizations, such as governments  and/or pharmaceutical companies.

To date, none of the studies funded by drug companies separate women who take oral contraceptives from women who have abortions. Imagine a tobacco company comparing lung cancer risks among pipe smokers to non-pipe-smokers without ever asking about cigarettes. That's what you get when a drug company simplistically compares women who terminated their pregnancy to women who avoided pregnancy... somehow. You have to ask about the Pill!

Not all studies have been funded by big drug companies, however, resulting in a steady drip of studies with elevated breast cancer risks after abortion. How can scientists ignore this? The answer is something called "recall bias." Abortion is such a private matter that healthy woman don't usually want to disclose it. All that changes when a woman gets cancer, however. If all the healthy women "forget" their abortions and all the sick women remember them, it would look like sick women had had more abortions even if they didn't really.

Between small numbers, recall bias, oral contraceptives, and the red-hot politics of abortion, all this can be confusing. Reasonable scientists have been able to disagree about the abortion/cancer link, and, as a result, American women have been choosing abortion for the last 32 years without finding out about this issue. But the latest research from China clears away the confusion.

Time Magazine reports that only 1.2% of Chinese women take the Pill, resulting in a lot of pregnancies. With China's "one-child per couple" policy, that has led to 13 million abortions every year. Unlike America, where these abortions are a "private matter between a woman and her doctor," Chinese data on abortions are kept by the same government agencies that conduct the procedures. With such huge numbers, official government data, and virtually no oral contraceptives, Chinese research on the abortion/breast cancer link should be as solid as research on living human beings can ever ethically be.

And the latest research devastates the claim that there is no link between abortion and breast cancer. The newest study from China perfectly matches the evidence from earlier studies suggesting that each week of a terminated pregnancy raises a woman's transient risk by approximately 3%. For a single abortion at 15-weeks, one would expect a 45% increase in risk. The meta-analysis reports a 44% rise. A second abortion would add more exposure, adding more risk. Two abortions in China leads to a 76% increase in risk. A third abortion would raise the risk even more--and Chinese women with three abortion had an average increased risk of 89%. This kind of "dose-response relationship" is very persuasive to open-minded researchers... especially when the "dose" is something with such a clear-cut relationship to breast cancer as estrogen.

Do you think this is going to change any medical minds? It will--but not in America any time soon. But that no longer matters. China has too many women and too many scientists to wait around for American "researchers" any longer.

Oral Contraceptives and Cancer

The National Cancer Institute admits there is some evidence that women who use oral contraceptives face an increased risk of breast cancer for several years. That is no surprise, since the Pill delivers estrogen to a woman's body, and increased exposure to estrogen is associated with elevated breast cancer risk. The mystery is not that oral contraceptives raise breast cancer risk, but that they don't appear to raise the risk anywhere near enough to account for the global epidemic of breast cancer since they became widely available in the 1960s.

What the National Cancer Institute won't tell you is that oral contraceptives are just one way a woman can get an abnormal exposure to estrogen. Pregnancy also delivers "sudden and dramatic increases in estrogen." There's nothing abnormal about pregnancy, of course, but doctors are well aware of a "transient" increase in breast cancer risk after birth. A full-term pregnancy matures and specializes breast tissue, reducing a woman's lifetime risk of breast cancer--but only after an elevated risk for the fifteen years after birth.

If a full-term pregnancy raises risk in the short term but lowers risk overall, what about an interrupted pregnancy? Miscarriages, which are often associated with insufficient estrogen levels, don't seem to have a measurable effect on breast cancer risk, but interrupting a viable pregnancy seems to produce the worst of both worlds--elevated short-term risk (due to estrogen) without the long-term benefit of mature, milk-producing tissue. In other words, it would seem that abortion must increase the risk of breast cancer in young women.

How come you don't hear that from the National Cancer Institute? The reason may disturb you. Study after study has been published on the abortion/breast cancer link, with varying results. Some, such as the most recent meta-analyis from China, find an elevated risk of cancer after abortion.

A systematic review and meta-analysis of 36 Chinese studies by Dr. Yubei Huang and his colleagues in the prestigious journal, Cancer Causes Control, last week reported a significant 44% increased breast cancer risk among women with at least one induced abortion...

Others find no increase in risk--but those studies simply compare women who have abortions to women who don't have abortions. That's like comparing pipe smokers to non-pipe-smokers instead of comparing pipe smokers to cigarette smokers to non-smokers. If estrogen is what elevates the risk of breast cancer, it makes no sense to compare one group of women with elevated estrogen levels (pill takers) to another group of women with elevated estrogen levels (whose pregnancies were terminated by induced abortions).

Once you include all sources of elevated estrogen, the "global epidemic" of breast cancer suddenly makes sense. Breast cancer is on the rise among all groups that routinely use oral contraceptives or choose abortion, while it tends to remain at normal levels among women without an artificially high exposure to estrogen.

If this is true, why isn't everybody talking about it? First of all, in our ultra-politicized world, anybody who mentions the abortion/breast cancer link is instantly marginalized--just like Sarah Palin was when she claimed Obamacare would lead to death panels. (If you haven't noticed, the mainstream media finally admits that death panels are real.)  Second, many of the biggest (and most questionable) studies on abortion and breast cancer have been funded by the same drug companies that produce the Pill. And finally, the political and legal implications of an abortion/breast cancer link are overwhelming. At a minimum, Planned Parenthood would be bankrupted by malpractice suits, and Roe v. Wade itself would have to be reconsidered in light of a genuine medical danger. The stakes in America are too high to let science be science.

But that can't be all there is to it! Science is science, and even the tobacco industry had to hide the evidence that smoking led to cancer. How can drug companies hide the evidence of an abortion/breast cancer link? The answer is, they don't. They just attribute it to "recall bias," arguing that women who choose abortion tend to be ashamed of their choice, and so don't tell the truth about their own medical history until they get cancer--at which point, life trumps privacy. With this approach, study after study that shows an elevated risk can be ignored every time. Without direct experiments on living human beings (which violates every principle of medical ethics), indirect evidence of increased risk gets ignored time after time.

Except in China. Abortion there has none of the personal stigma that it has in the United States, and medical records on abortions are easily available. With nearly a billion people and a state-mandated one-child per couple policy, China is the next best thing to a laboratory for conducting direct experimentation on living human beings. This makes it especially significant that Chinese researchers are pointing out the consistent elevated risk after abortion.

Convinced?  Then tell a friend--or ten. Forward this link to folks who need to know.

Skeptical? I haven't scratched the surface of the evidence for this link. Post your questions or critiques in the comment section below and I'll respond to them as time permits.

Angry?  That's what the comments are for--but please keep it clean, or I'll delete it, whether you're roasting me or toasting me. This blog is intended for the whole family, with a zero tolerance policy on profanity.