Yet another study shows no link between abortion and breast cancer

Last summer, I mentioned that groups receiving federal funding were providing misleading information about abortion, including the unsupported statement that having an abortion increases the risk of development of breast cancer. As I noted, this "link" has been refuted by a number of analyses, including a 2004 Lancet paper and a 2003 National Cancer Institute report. As if those weren't enough, a new study comes to the same conclusion: yep, no link. More after the jump.

The new study, appearing in Monday's Archives of Internal Medicine, looked at data from 105,716 women participating in the Nurses' Health Study, which was established in 1976 to study a wide range of health issues affecting women.

The women, ages 29 to 46 at the start of the study, were followed for 10 years. Every two years, they were asked about abortions, miscarriages and new breast cancer diagnoses. The researchers looked at medical records to confirm the diagnoses.

Unlike some of the early studies which suggested a link between abortion and breast cancer, many subsequent ones have relied not on the recollection and self-reporting of abortion in cases and controls (which can introduce bias), but rather examine medical records (and in this case, other survey data) that was collected prior to diagnosis with breast cancer.

Like prior studies, the authors found that having a completed pregnancy, and breast-feeding, were protective when it came to the subsequent development of breast cancer. The authors found no association between either spontaneous abortion (miscarriage) nor abortion and breast cancer. However, there will always be those who stick to their opinions despite the evidence, rather than because of it. For the abortion-breast cancer ("ABC") connection, this dissenter is Dr. Joel Brind of Baruch College. Dr. Brind was the lone participant in the 2003 NCI conference who disagreed with the conclusions of the summary report, and argues that the current study is "severely flawed" by not allowing sufficient follow-up time in women who experienced fairly recent abortions:

[Brind] said the new study is flawed because it included very recent abortions -- too recent for them to contribute to the development of cancer. Including those abortions in the analysis may have diluted the cancer rates, he said.

And this is a legitimate criticism; the authors could have limited the study to abortions obtained at least a decade ago or more. However, Karin Michels, the lead author, notes that "...more than 90 percent of the abortions in the study occurred before 1993." Therefore, even eliminating those later abortions would be unlikely to have significantly altered the conclusions.

And for those who follow the evolution/creation fight, the thimerosal/autism brigade, or the HIV "dissidents," this line of argumentation may sound familiar:

The U.S. National Cancer Institute (NCI) funded the new study, Michels et al. 2007. Ten years ago, NCI expert Patricia Hartge concluded, "In short, a woman need not worry about breast cancer when facing the difficult decision of whether to terminate a pregnancy."

"So why has the NCI continued to spend millions of dollars to fund studies on the abortion-cancer link?" asked Malec. "Clearly, its scientists must either suspect a link or know that it exists."

Ah, yes...we continue to research something, therefore we must "know" that we're already wrong about our prior conclusions. Scientists write about the claims made by intelligent design creationists; therefore, the creationists are correct! The government removed thimerosal from vaccines; therefore, they must know that it really caused autism! Scientists refine their understanding of HIV/AIDS as new research comes to light; therefore, they're all wrong about everything previously!

The ABC folks, however, put the icing on the cake by adding this piece of strained logic:

"Even the NCI agrees that increased childbearing, starting at an early age, protects women from breast cancer," said Malec. "Legislators have a moral obligation to require abortion providers to inform expectant mothers that if they have an abortion, their breast cancer risk will be higher than it would be if they have a baby. That's settled science."

And indeed, as noted right in the paper: "A full-term pregnancy before the age of 35 years reduces long-term risk of breast cancer." This isn't anything that's hidden. However, they're being disingenuous when they say that the breast cancer risk of these women would be "higher than it would be if they have a baby." Indeed, sure, if these women go on to never give birth to children, they will lack the *protective* effect that childbirth provides. However, that's like telling me that I'm increasing my risk of breast cancer when I'm out with friends and I abstain from wine while the others around me have a glass of merlot. If the women follow their aborted pregnancy with one or more completed pregnancy before the age of 35, however, they will experience the same protective effect as others in their cohort who never obtained an abortion. It's not the abortion itself that is a risk factor that predisposes to breast cancer; it's the completion of a pregnancy that helps to *protect* against it.

Now, one may argue that these are two sides of the same coin, but imagine this scenario (exaggerated for emphasis): a woman has 10 pregnancies between the age of 16 and 26. She ends them all by obtaining an abortion. Then she goes on to have 5 children between the ages of 27 and 35. Because she followed the abortions she obtained with completed pregnancies, she'll still have a lower risk of breast cancer than a woman who never had an abortion but also never had any children. It's not the abortion that makes the difference; it's the childbearing. Of course, I don't expect the ABC group to start advocating for these types of disclaimers to be discussed during abortion counseling anytime soon.

Reference

Michels et al. 2007. Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Women. Arch Intern Med. 168:814-20.