(LifeWire) - Although emotions shouldn't play a role in fact-based scientific research, for years this appears to have been one by-product of the controversy over abortion. The moral-religious-political debate obscured our understanding of the relationship between abortion and breast cancer, until research in the past two decades established there's no increase in a woman's risk for this much-feared cancer by terminating a pregnancy.
The first studies that analyzed breast cancer in relation to reproductive issues date back to the 1920s, but it wasn't until the 1950s that Japanese researchers started calculating the impact of spontaneous and induced abortions on the chances of developing the disease. Breast cancer is currently the most common cancer in women, with more than 240,000 women being diagnosed each year.
Spontaneous abortion, better known as miscarriage, occurs when the body expels a fetus before 20 weeks of gestation. (After 20 weeks, pregnancy losses are termed preterm deliveries or stillbirths.) An induced abortion is the intentional termination of a pregnancy.
With 1.3 million abortions performed in the United States every year and 35% of women undergoing an abortion before they reach the age of 45, it makes sense that researchers would seek to determine whether there was any relationship between abortion and breast cancer.
But the abortion controversy has made research in this area more difficult, affecting both how patients reported (or failed to report) aspects of their medical histories and how researchers used this information. As a result, the findings were skewed in favor of the theory that women who had, had abortions were more likely to get breast cancer.
Regardless of the times, research has always focused on the changes breast tissue undergoes as pregnancy begins and progresses. Pregnancy spurs a woman's breasts to prepare for breastfeeding by using increasing levels of the hormones estrogen, progesterone and prolactin to promote cell growth in the milk ducts — scientists wondered if the risk of breast cancer could increase from the abrupt interruption of this process after an abortion.
In the early years after Roe v. Wade, women's reluctance to divulge their reproductive past made it difficult to retrieve accurate information about abortion and its relationship — if any — to breast cancer. Once diagnosed with breast cancer, patients were often more willing to disclose past abortions in hopes that a cause for their cancer could be established. Healthy women, on the other hand, were less likely to divulge past abortions. This discrepancy, called "recall bias," weakened the accuracy of many studies done until the 1990s.
Since that time, however, it has become more socially acceptable for women to be open about their reproductive histories. Scientists, as well, have changed their approach to this research by studying groups of cancer-free women over long periods to see which individuals later develop breast cancer. Since their backgrounds were established before the onset of breast cancer, the "recall bias" was not a factor and results became more accurate.
Over the past two decades, many large studies have been performed worldwide using a more reliable research model to determine abortion and breast cancer relationship. The largest of these studies was reported in 2007 in the Archives of Internal Medicine and included 1.5 million women born between 1935 and 1978. Also in 2007, Harvard researchers reported findings based on more than 100,000 women who were followed for 10 years. Neither study found any evidence of a link between induced abortions and breast cancer.
Sources:
"Abortion, Miscarriage and Breast Cancer Risk." cancer.gov 2008. National Cancer Institute. 1 Jul. 2008.
"Can Having an Abortion Cause or Contribute to Breast Cancer?" cancer.org. 6 Aug. 2007. American Cancer Society. 1 Jul. 2008.
Jasen, Patricia. "Breast Cancer and the Politics of Abortion in the United States." Medical History 49:41 Oct. 2005 423-444. 1 Jul. 2008.
Michels, Karin. "Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Women." Archives of Internal Medicine 167:823(2007): 814-20. 1 Jul. 2008.
"Miscarriage." MedlinePlus. 19 Sep. 2006 National Library of Medicine, National Institutes of Health, 14 Jul. 2008.
Wright, Alexi and Ingrid T. Katz. "Roe Versus Reality -- Abortion and Women's Health." New England Journal of Medicine 355:16(2006): 1-9. 1 Jul. 2008.
