April 24, 2002

It has been claimed that induced abortion is linked with an increased risk of subsequent breast cancer. Is this a real risk of which every woman considering elective abortion should be appraised? Or is it simply an unproven threat thrown into the abortion arena to frighten pregnant women from choosing an induced abortion? These are absolutely vital questions for any pregnant woman contemplating an induced abortion. The answers to these questions determine whether the threat of breast cancer, surgery, radiation, chemotherapy, and even death, hangs over the choice to have an induced abortion. We must depend on "evidence based medicine" to guide us to valid conclusions on these issues.

Here is the evidence:
 
There are two independent pregnancy-related factors for breast cancer noted in the medical literature. The first is a protective effect, against breast cancer, of an early first full term pregnancy. The landmark study demonstrating this protective effect [MacMahon, et al, (1970) Bull WHO 43:209-221] is widely accepted in the medical world. This research group also found that each one year delay in the first full term pregnancy increased relative breast cancer risk by 3.5% (compounded)[Trichopolous D, Hsieh C, MacMahon B, Lin T, et a., Age at any Birth and Breast Cancer Risk, International J Cancer, 1983:31:70l-704]. Therefore, aborting a first pregnancy eliminates the protective effect that that pregnancy would have provided against breast cancer if not aborted.
 
The second independent risk factor for breast cancer is induced abortion. As of March, 2002, there have been 37 studies published in the worldwide medical literature reporting data on the risk of breast cancer among women with a history of induced abortion. Twenty-eight of these studies report an increased risk. In the United States, there have been 15 such studies, 13 of which report increased risk, 8 with statistical significance (at least 95% probability that the association is not due to chance). These findings were true irrespective of the age at first full-term pregnancy. The relative risk increase of the 37 studies combined is 30%. This means that among aborted women there would be a 30% increase in breast cancer cases over what would normally be expected. In the current American context this would result in approximately 5,000 additional cases of breast cancer per year as there are about 190,000 new cases of breast cancer diagnosed in the US each year.)
 
Consider the implications of a study funded by the United States National Cancer Institute to investigate any effect of induced abortion on the risk of breast cancer (Daling et al, l994, JNCI 86:1584-92). This study found an overall 50% increase in breast cancer risk by age 45 for women who have had an induced abortion. American women today have an approximate 12% lifetime chance of developing breast cancer. It follows that those who have had an induced abortion will have an 18% lifetime chance of developing breast cancer. But the risk increases even more for certain subgroups. For example, among women with a family history of breast cancer (mother, grandmother, sister, or aunt), the increase in risk is 80%. If the woman had her abortion before she was age 18, the increase in risk is more than 100%! If the woman had both risk factors (family history of breast cancer, and abortion before age 18), the risk was incalculably high, i.e., there were 12 such women out of 1800 in the study, and all twelve developed breast cancer by age 45.

Despite this preponderance of data there are authoritative figures in prominent national institutions such as the National Cancer Institute and the American College of Obstetricians and Gynecologists who trivialize, or even deny, these findings. They generally cite the epidemiologic concept of "recall bias" as the explanation for why they don’t accept the bulk of the medical and scientific literature on the subject.

Recall bias is also known as "reporting bias" or "response bias". What is it that makes it so powerful in this matter that it could possibly negate the findings of so many studies from around the world? Recall bias is simply the presumption that women who have breast cancer will be more honest when asked if they have ever had an abortion, whereas healthy women will be less honest if asked the same question. Thus, they argue, in interview-based studies, the incidence of breast cancer will be falsely higher in the women with previous abortions. Recall bias is a real phenomenon which has been demonstrated in other circumstances. However it has yet to be clearly demonstrated in this subject. A Swedish study published to demonstrate such a "recall bias" in the matter of abortion and subsequent breast cancer risk, was published in the American Journal of Epidemiology in 1991. This is the only paper we are aware of which claimed to show statistically significant evidence of "recall bias." They reported that eight breast cancer patients had imagined (and reported) an abortion for which there was no computerized record. Importantly, the Swedish team retracted the idea of over-reporting in the March, 1998 issue of JECH, rendering their “finding” of recall bias not statistically significant. Apparently these women had their abortions in a neighboring country, and therefore they were not documented in the Swedish computer record.

Therefore, we currently are aware of no studies that have substantiated, with statistical significance, the charge of recall bias in regard to induced abortion and the risk of breast cancer. In fact, the only study published on American women which relied solely on data from medical records entered at the time of the abortion (and therefore not subject to “recall bias”) reported a statistically significant 90% increase in breast cancer risk with induced abortion. (Howe et al (1989) Int J Epidemiol 18:300-4.)

With regard to the induced abortion-breast cancer risk controversy, the subject of "recall bias," has taken on a life of its own, out of proportion to any demonstrated significance, and has become the rallying cry for anyone who desires to summarily dismiss the world's literature on the subject.

Consider the following:

 
The American College of Obstetricians and Gynecologists 2002 Compendium of Selected Publications, states "Long term risks sometimes attributed to surgical abortion include potential effects on reproductive function, cancer incidence, and psychological sequelae. However, the medical literature, when carefully evaluated, clearly demonstrates no significant negative impact on any of these factors with surgical abortion" (pg. 392).

In the March 2002 issue of Obstetrics and Gynecology Clinics of North America, there is a 10 page review article titled "Risk factors for breast cancer." In this article, only the following sentence mentions abortion: "Much has been written regarding the risk of breast cancer and induced abortion; however, an analysis of current data reveals no relationship of induce abortion to breast cancer risk."

The National Cancer Institute's March 6, 2002 web page, under "Cancer Facts," section on "Abortion and Breast Cancer" denies an abortion-breast cancer link.

On this vital issue, organized medicine, for reasons of its own, is apparently willing to ignore or deny the evidence. We find this unacceptable. Women's health, even their lives, may be at risk.

Ultimately, evidence based medicine (and truth) will prevail--but too late for many women who are submitting to induced abortions without informed consent regarding any potential breast cancer risk. This is all done with the assurances of many leaders in women's health care that women need not worry about such risk.

 If the 28 of 37 worldwide studies, including 13 of 15 American studies, are correct, physicians who have denied or ignored an abortion-breast cancer link will stand guilty of great disservice to the women they purport to serve--especially to those who subsequently develop breast cancer.
 
Counselors or doctors dealing with a pregnant woman considering abortion can confidently inform her that:
 
 1. Interruption of her first pregnancy will remove the protective effect of that first full term pregnancy, and subject her to a small but real increased risk of developing breast cancer in the future compared to the risk she would have if she carried the pregnancy.
 
 2. According to the only study published specifically funded by the United States National Cancer Institute to investigate any abortion-breast cancer association, there is an overall 50% increase in the subsequent risk of breast cancer, following an induced abortion. If a woman has a mother, sister, aunt or grandmother with breast cancer, she will increase her chance of getting breast cancer by 80%, if she is under l8, she will double her chance of getting breast cancer, and if both conditions pertain, her risk is much higher (12 of 12 in that study). These cancers were diagnosed by age 45.

 3. 75% of the world's scientific literature on the subject, and 87% of the American scientific literature on the subject (62% statistically significant), suggest a conclusion that induced abortion is associated with a significant increase in the risk of developing breast cancer in later life.