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.