An induced abortion raises a woman's risk of developing breast cancer by age 45 at least 50%, and by three times that if she is under 18 when the abortion occurs, according to a large new study by Seattle epidemiologists.
But breast cancer experts cautioned that the new report contains many caveats and it is not clear that the results apply to the vast majority of women because only 13% of breast cancer cases occur before 45.
The study, scheduled to be published next week in the Journal of the National Cancer Institute, is the latest, and the largest, in a series of about 20 reports on the association between breast cancer and abortion. About half of those have suggested a causal link, but most experts feel the issue is far from resolved.
"The Seattle study is a very definite step in the right direction," said Dr. Louise Brinton of the National Cancer Institute. "I think that it raises concern about the risks of induced abortions . . . but it doesn't resolve the issue."
Eugenia Calle of the American Cancer Society added: "We are still left with an area of research where there is very little that is falling together to form a cohesive, consistent picture. There is a great deal of work that needs to be done before the scientific community will feel comfortable saying that induced abortions are or are not a risk factor" for breast cancer.
Anti-abortion groups, which have seized the issue of a link between abortions and breast cancer as a powerful tool for promoting their opposition to the procedure, hailed the new study. "It's an important contribution to this area that we think needs to be looked at very closely," said Wanda Franz, president of the National Right to Life Committee. "Given the seriousness of the disease . . . any factor like this needs to be treated seriously and pursued. . . . We're very concerned that women need to know everything about the risks because they are being asked to make a serious choice" in opting for an abortion.
But Pamela J. Maraldo, president of the Planned Parenthood Federation of America countered: "The fact remains that there is no consensus among researchers as to whether there is a cause-and-effect relationship between abortion and breast cancer."
Suellen B. Wood of Planned Parenthood Los Angeles added, "We will continue (to perform abortions) until there is much more definitive information that would lead us to change our opinions."
An estimated 182,000 American women develop breast cancer each year, with 46,000 dying of it--making it the second most deadly form of cancer in women, after lung cancer.
Researchers do not know what causes breast cancer. Genetics plays a strong role in the inherited form of breast cancer, but its role in the majority of non-inherited cases of the disease is still debated. Other risk factors include an early age of menarche, late age at menopause, not having children or having the first child late in life, socioeconomic status and consumption of dietary fats.
Animal studies suggest that abortion could also be a risk factor. Studies in rats show that breast cells proliferate rapidly during the earliest stages of pregnancy. If the pregnancy is ended suddenly, many of these proliferating cells remain, primed to continue replicating if triggered by a carcinogen or some other environmental factor. If the pregnancy proceeds to completion, however, the cells lose that priming and are more difficult to activate.
Epidemiologist Janet R. Daling and her colleagues at the Fred Hutchison Cancer Center in Seattle studied 854 white women, born after 1944 and living in western Washington, who developed breast cancer between 1983 and 1990. That age group was selected because abortion was legal during their reproductive years. The women were compared to a control group of 961 women who did not have breast cancer.
The team found that, overall, women who had an abortion were 50% more likely to develop breast cancer. If the abortion was before age 18, the women were 150% more likely to develop breast cancer, and the risk was higher still if the pregnancy had proceeded beyond eight weeks or if the women had a family history of breast cancer. Women who were over 30 at the time of an abortion had a 110% increase in risk.
But the study had some contradictions as well. The team saw no effect on risk arising from spontaneous abortions. If the biological theory on risk is correct, spontaneous abortions should be no different from induced abortions in influencing breast cancer. They also saw no further increase in risk from multiple abortions . This observation also contradicts theory.
Other potential problems include the reliability of women's self-reports of abortion--previous studies had reported that a significant number of women do not admit having abortions. In addition, 13% of the women with breast cancer could not be interviewed because they had died or left the area.
Most researchers conclude that women should not be unduly concerned about the study. Epidemiologist Noel Weiss, one of the study's authors, said: "I personally would not be alarmed because I know that this study will need to be replicated and may not necessarily reflect the true state of affairs."
Weiss also noted that the number of women who develop breast cancer before age 45 is 4 out of every 100,000. Even if their results are correct, he added, the number would increase only to 6 per 100,000.