Study finds less heredity link for breast cancer

July 21, 1993|By New York Times News Service

In recent years, support groups for women at increased risk for breast cancer have proliferated, filled with terrified women who have a mother or sister who succumbed to the disease. Now a new study suggests that such women, while somewhat prone to breast cancer, are not as susceptible as was previously thought.

While some prior studies had found that women with breast cancer in their immediate family were three times more likely to develop breast cancer than other women, the new research indicates that their risk is probably only about twice that of those without a family history of the disease.

What's more, of the 2,389 women with breast cancer in the current study, only 2.5 percent of cases could be attributed to a family history of the disease.

"What this all points to is that women with a single family member should be counseled and treated in the same way as women without a family history," said Dr. Graham A. Colditz, associate professor of medicine at the Channing Laboratory of Harvard Medical School and the study's lead author.

The study, which appears in today's issue of the Journal of the American Medical Association, involved 117,988 women whose health histories and habits have been followed by a team of Harvard researchers at the Brigham and Women's Hospital since 1976 as part of the Nurses' Health Study.

Of these women, who were 30 to 55 years old at the start of the study, 2,389 had developed breast cancer by 1988.

Since the researchers had previously collected extensive health information about each participant's family, they determined that having a mother with breast cancer did increase somewhat the risk that a woman would get the disease and that the level of risk was highest if the mother had died of breast cancer at an early age.

Women whose mothers had gotten breast cancer before the age of 40 were 2.1 times as likely as other women to get the disease; for those whose mothers developed breast cancer after the age of 70, the risk was only 1.5 times as great.

Women with a sister with breast cancer were 2.3 times as likely to get breast cancer as women without a family history. But even women with the strongest familial predilection toward breast cancer -- with both mothers and sisters affected -- were only 2.5 times more likely to get the disease than women without family risks.

While the current study is huge and free of many of the design problems that have plagued previous studies about the genetics of breast cancer, some specialists say the results are neither surprising nor dramatically different from those of the past.

"There is a misconception about how much of breast cancer is due to hereditary factors, both on the part of the public and some physicians who are recommending that women get prophylactic mastectomies for a family history of the disease," said Dr. Louise Brinton, chief of the environmental studies section of the National Cancer Institute.

"Hopefully the paper will bring to the forefront that only a small proportion of breast cancer is attributable to genetics."

She and other experts say that the misguided belief that breast cancer is largely hereditary has led to irrational responses to the disease, causing women who have a family history to worry unduly and those who do not to feel they are immune, forgoing breast examinations and mammograms.

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