The Abortion/Breast Cancer Link

Dr. Chris Kahlenborn answers frequently asked questions about the link between abortion and breast cancer.

Q:A: Why would a woman who has an induced abortion before her first full-term pregnancy (FFTP) suffer an increased risk of developing breast cancer?

A woman's breast is especially sensitive to carcinogenic (i.e., cancer producing) influences before she delivers her first child. When a woman becomes pregnant, a number of hormone levels increase dramatically in her body. Three especially notable ones are estradiol, progesterone (i.e., the female sexual hormones), and hCG (human Chorionic Gonadotropin). All of these hormones, especially the latter, serve to stimulate immature breast cells to mature into fully differentiated cells [1]. If this process is artificially interrupted by way of an induced abortion, the hormone levels drop suddenly and dramatically, thereby suspending the natural process of maturation of many of the woman's breast cells. This is referred to as a "hormonal blow" by researchers. These cells are now "vulnerable" to carcinogens because they started the maturation process but were never able to complete it. (Cells that have fully matured are less vulnerable to carcinogens than cells that are in the process of maturation).

Q-B: Do any animal models support the claim that abortions early in life increase breast cancer risk?

Yes. Russo and Russo, in their classic work published in 1980 [2], studied several groups of rats which were given a specific carcinogen (cancer producing agent) called DMBA. They noted that 77% of the rats who underwent an abortion developed breast cancer and 69% of the virgin rats developed breast cancer, but 0% of the rats who were allowed to complete their pregnancy developed breast cancer.

Q-C: Could you tell me about the history of the abortion/breast cancer debate?

As early as 1957, Segi et al noted that women who had induced abortions had at least a 2-fold increased risk of breast cancer [3]. In 1981, Pike et al [4] published their notable work showing that young women (under the age of 32) who had experienced an abortion before their first full-term pregnancy (FFTP) had a 140% increased risk of breast cancer. A number of studies followed but in 1994, Daling et al [5] published a large study which noted that women who had an abortion before their FFTP suffered a 40% increased risk. This risk increased to 150% if the adolescent had her abortion before the age of 18. In addition, Daling et al noted that if adolescents under the age of 18 aborted a baby that was more than 8 weeks old, they suffered an 800% increased risk of developing breast cancer.

Finally, in 1996, in what is openly regarded as the most meticulous and comprehensive meta-analysis (i.e., a synthesis of all the major studies done in a particular field concluding in an overall risk for the pooled studies) of all the abortion/breast cancer research articles ever done, Brind et al [6] found that women who had an abortion before their FFTP had a 50% increased risk of developing breast cancer whereas women who had an abortion after their FFTP sustained a 30% increased risk.

Q-D: If Dr. Brind et al's study was so conclusive, then why is the subject still being debated?

Because of the controversy regarding abortion, Dr. Brind's study came under intense scrutiny; however, the results seemed irrefutable. Janet Daling - a prominent epidemiologist (a researcher who studies trends in the medical field) - was quoted in the Wall Street Journal as stating that Brind et al's results were "very objective and statistically beyond reproach." [7] Then in early 1997, the New England Journal of Medicine published the results of a large prospective study by Melbye et al [8] which claimed to show that abortion did not increase the risk of breast cancer.

Q-E: Was there any problem with the study by Melbye?

Yes. It is astonishing that the New England Journal of Medicine allowed it to be published in its submitted form. It had several glaring problems that have been pointed out in a follow-up letter to the New England Journal of Medicine [9]. The main ones include the following: 1) Melbye's data actually pointed to a 44% increased risk of breast cancer due to abortion, but they never printed this result; 2) The follow-up period for the "cases" (i.e., women who had an induced abortion) was less than 10 years, whereas it was over 20 years for the "controls" (i.e., women who did not have an induced abortion). A follow-up period of less than 10 years is not long enough to show the effect of an abortion (i.e., too short of a latent period); 3) Over 30,000 women in the study who had abortions were "misclassified" as not having them - thus 30,000 women were counted as not having abortions, when in fact they really had abortions; and 4) The study did note that women who had an abortion after the 12th week sustained a 38% increased risk of breast cancer, whereas women who had late-term abortions (i.e., after 18 weeks) had a statistically significant increase of 89%. Both of these results received little media attention.

1. Russo J, Russo IH. Toward a physiological approach to breast cancer prevention. Cancer Epidemiology, Biomarkers and Prevention. 1994; 3: 353-364.

2. Russo J, Russo IH. Susceptibility of the mammary gland to carcinogenesis. Am J Pathol. 1980; 100: 497-512.

3. Segi M, et al. An epidemiological study on cancer in Japan . GANN . 1957; 48: 1-63.

4. Pike MC, Henderson BE, et al. Oral contraceptive use and early abortion as risk factors for breast cancer in young women. Br J Cancer. 1981; 43: 72-76.

5. Daling J, Malone K, et al. Risk of breast cancer among young women: relationship to induced abortion. J Natl Cancer Inst . 1994; 86: 1584-1592.

6. Brind J, Chinchilli M, et al. Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-analysis. J Epidemiol Community Health. 10/ 1996; 50: 481-496.

7. Lagnado L. Study on abortion and cancer spurs fight. Wall Street Journal . Oct. 11, 1996 .

8. Melbye M, Wohlfahrt J, et al. Induced abortion and the risk of breast cancer. N Engl J Med . 1997; 336: 81-85.

9. Brind J, et al. Induced abortion and the risk of breast cancer. N Engl J Med . 1997; 336: 1834.

Excerpted from "Overview: Abortion and Breast Cancer" from the Polycarp Institute's website, www.polycarp.org . Reprinted with permission.