Risk Set Right

New Studies Show no Association Between Induced or Spontaneous Abortions and Breast Cancer Risk.

by Jon Nalick

The relationship between induced and spontaneous abortion and breast cancer risk has been the subject of extensive research beginning in the late 1950s. Until the mid-1990s, the evidence was inconsistent, with some studies suggesting no increase in risk of breast cancer among women who had an abortion and others suggesting a small increase in risk.

But a scientific advisory panel convened by the National Cancer Institute (NCI) has concluded that having an abortion does not increase a woman’s breast cancer risk later in life.

Most of these early studies were flawed in a number of ways that can lead to unreliable results, says Leslie Bernstein, Ph.D., the AFLAC Chair in Cancer Research at the Keck School of Medicine of USC, and a member of the NCI’s Early Reproductive Events and Breast Cancer Workshop and the NCI Board of Scientific Counselors.

In many of these studies, only a small number of women were included and the data were collected only after breast cancer had been diagnosed. Also, women’s histories of miscarriage and abortion were based on their “self-report” rather than on their medical records. Breast cancer patients, trying to understand what led to their diagnoses, would be more likely to report accurately having an abortion than would healthy control women in studies where much of the woman’s reproductive history was prior to legalization of abortion. Such bias would artificially show that induced abortion increased breast cancer risk when it actually does not.

How an induced abortion was linked in previous studies to increased breast cancer risk—and why a full-term pregnancy protects against cancer, as believed—is not fully understood, Bernstein says. “Previously, the hypothesis put forth was that a full-term pregnancy is needed to complete differentiation of the breast tissue, and that interruption of this process is harmful. But other mechanisms may be the reason for protection of full-term pregnancies and those processes may occur earlier in pregnancy and may not be affected by incomplete pregnancies.”

Recent studies are more carefully designed and better able to address the issue of any relationship, Bernstein says.

These newer studies examined large numbers of women, took into account a woman’s overall pregnancy history in making valid comparisons and some collected data before breast cancer was found and gathered medical history information from medical records rather than simply from self-reports, thereby generating more reliable findings. The newer studies consistently showed no association between induced or spontaneous abortions and breast cancer risk.

Among the best evidence is a landmark Danish study that used computerized medical records to compare women who had abortions with that country’s cancer registry—and found no higher cancer rate.

At present, the factors known to increase a woman’s chance of developing breast cancer include age (a woman’s chances of getting breast cancer increase as she gets older), family history of breast cancer, early age at first menstrual period, late age at menopause, late age at the time of birth of her first full-term pregnancy or having no full-term pregnancy, and certain breast conditions. Obesity is also a risk factor for breast cancer in postmenopausal women. Exercise is now recognized as one means for reducing breast cancer risk, as is limiting alcohol intake and breast-feeding infants for a long period.

The NCI recommends that women receive mammography screening every year or two, beginning in their 40s. Women who have a higher-than-average risk of breast cancer (for example, women with a family history of breast cancer) should seek expert medical advice about whether they should be screened before age 40, and how frequently they should be screened.

The panel’s full report is available online at http://www.cancer.gov/cancerinfo/ere-workshop-report

 

RELATED ARTICLES

reproductive events and risks
The conclusions of the scientific advisory panel convened by the National Cancer Institute, which contradict some earlier studies that found varying degrees of additional risk associated with abortion, represent facts considered by the panel to be “well established” by epidemiologic and other studies.
Among the conclusions reached by the panel were that:
- delivering a full-term baby early in life lowers breast cancer risk later in life;
- neither induced abortion nor miscarriage boosts risk of breast cancer;
- women who never give birth have about the same lifetime risk of breast cancer as a woman whose first birth occurs around age 30; and
- long duration of breast-feeding lowers breast cancer risk.