Under pressure from abortion opponents, NCI has weakened its assessment of published research examining whether having an abortion changes a woman’s risk of developing breast cancer.

A statement posted on the NCI Web site Nov. 25 draws no conclusion about breast cancer risk in women who have had abortions, and characterizes the available data as “inconsistent.”

More than 30 published studies since 1957 have examined the “possible relationship between abortion and breast cancer,” the statement said. “Some studies have reported statistically significant evidence of an increased risk of breast cancer in women who have had abortions, while others have merely suggested an increased risk. Other studies have found no increase in risk among women who had an interrupted pregnancy.”

That ambiguous statement contrasts sharply with a “fact sheet” posted on the Institute’s Web site last March, which concluded that “the current body of scientific evidence suggests that women who have had either induced or spontaneous abortions have the same risk as other women for developing breast cancer.”

The earlier statement discussed the largest and most reliable cohort study, reported by Danish researchers in the New England Journal of Medicine in 1997. That study used health information from registries for 1.5 million Danish women, was not subject to recall bias, and found that induced abortion had no overall effect on the risk of breast cancer.

The new NCI statement provides no information about this study.

It was not a change in scientific consensus that caused NCI to alter its statement. The Institute removed the fact sheet from its Web site last June after receiving a letter from Rep. Chris Smith (RNJ) and 27 other members of Congress known to oppose abortion. The letter demanded that NCI take down the fact sheet and claimed that most of the published studies show abortion increases the risk of breast cancer—an assertion that NCI disputed in a response to a Congressional inquiry in 1999 (The Cancer Letter, Vol. 28 No. 28, July 12, 2002).

The new statement is intended as an “interim statement” until the final report of an NCI workshop on early reproductive events and breast cancer, to be held next year, NCI spokesman Dorrie Hightower said.

“Further scientific research needs to be done to determine and to investigate the relationship of breast cancer to hormone changes that occur with pregnancy,” the new NCI statement said.

The NCI statement is posted at www .cancer.gov/cancer_information/doc.aspx?viewid=8cf78b34-fc6a-4fc7-9a63-6b16590af277.

In contrast, the American Cancer Society concludes that, “Research studies have not found a cause-and-effect relationship between breast cancer and abortion.”

An article posted on the society’s Web site notes that most of the early studies of abortion and breast cancer used a case-control study design, which is prone to recall bias. “Studies have shown that healthy women are les likely to report their histories of induced abortions,” the article said. “In contrast, women with breast cancer are more likely to accurately report their reproductive histories because they are literally searching their memories for anything that may have contributed to their disease.”

Also, induced abortions were illegal in the U.S. until 1973. Women in the earlier studies may not have wanted researchers to know they had an illegal abortion, the society said.

“It is likely that the small increases in breast cancer risk observed in many of these studies were not authentic findings because of recall bias,” the society said.

The ACS article said the Danish study’s size and methods “provides substantial evidence that induced abortion does not affect a woman’s risk of developing breast cancer.”

The society’s article said “false alarms” about breast cancer risk do not serve the public:

“The issue of abortion generates passionate personal and political viewpoints, regardless of any possible disease connection. Breast cancer is the second most common cancer in women, and it can be a life-threatening disease that most women fear. Still, the public is not well-served by false alarms, even with both the exposure and the disease are of great importance and interest to us all. At the present time, the scientific evidence does not support a causal association between induced abortion and breast cancer.”

The ACS statement is available at: www.cancer.org/docroot/CRI/content/CRI_2_6x_Can_Having_an_Abortion_Cause_or_Contribute_to_Breast_Cancer.asp