Study Refigures Odds of Getting Breast Cancer : Research: Narrowing the usual broad-brush approach, scientists have developed a method of calculating the risk factor of disease for an individual woman. The system is the first to combine four factors from a woman’s medical history.

What are a woman’s odds of developing breast cancer?

Millions of American women would like to know the answer. But the best that doctors have been able to offer are broad-brush estimates that often seem to have little specific relevance to the individual woman.

Now a team of researchers at the National Cancer Institute has developed a formula that can calculate a woman’s risk of developing breast cancer within the next 10 to 30 years, based on her medical history.

The new way of estimating individual risk is drawn from the Breast Cancer Detection Demonstration Project, a study of more than 5,000 women. A report of the new measure was published in the Dec. 20 issue of the Journal of the National Cancer Institute.

“This is a major advance in understanding the susceptibility to breast cancer,” said Daniel G. Miller, director of the Preventive Medicine Institute at the Strang Clinic in New York City. “It gives us reliable, predictive information about the likelihood of an individual woman developing breast cancer over a designated time interval.”

Until now, doctors could tell a woman whose mother had suffered from breast cancer that she too was at increased risk of developing the disease. But they had no way to calculate what her odds were of actually developing a tumor. Nor was there any way to take into account a woman’s other risk factors, such as at what age she began menstruating, which might increase--or decrease--her chances of developing breast cancer.

“There have been a lot of individual studies of breast-cancer risk factors,” said John Mulvihill, chief of the clinical genetics section at NCI and a co-author of the study. “But we now have the first approach of combining risk factors and seeing what a summary effect they have on an individual’s risk.”

To do that, researchers rely on an equation that takes into account four factors from a woman’s medical history: age when menstruation began, the number of negative breast biopsies she has had, her age at the birth of her first live-born child, and whether her mother or sisters have had breast cancer.

By offering women a much more precise idea of their actual risk, researchers and physicians hope to increase their use of mammography and monthly breast self-exams, as well as regular checkups by physicians. In addition, some women may be advised to lose weight, lower their fat consumption and give up alcohol, all of which have been linked in some studies to breast cancer.

Women with a family history of breast cancer “tend to overestimate their chances of getting breast cancer,” said the Strang Clinic’s Miller. They often develop tremendous anxiety about their risk and sometimes, he said, don’t take appropriate steps to limit it.

“They need a reliable estimate so that they can act in a rational manner,” he said. “It will help them comply with the recommendation for early detection.” Doctors could then target certain women for more frequent physical exams, weight loss, low-fat diets and, in extreme cases, preventive mastectomies.

One criticism of the study, noted in an editorial accompanying last week’s publication, was that it failed to take into account alcohol consumption and estrogen-replacement therapy. Both have been shown, in this study and some others, to increase the risk of breast cancer.

The new risk measure tells the average woman her likelihood of developing breast cancer, said Linda Williams Pickle, director of the Biostatistical Unit at Georgetown University’s Vincent T. Lombardi Cancer Research Center, “but for women who are at high risk, these will be underestimates.”

But the new model, by encouraging breast screening and boosting research in prevention, represents “a major step toward achieving breast-cancer control,” said Pickle and her colleague Karen A. Johnson, also of Georgetown, in the editorial.

The information also could help doctors make treatment decisions, such as whether to prescribe estrogen-replacement therapy to a particular woman. And it will help researchers design better studies of breast-cancer prevention.

“If you want to prevent breast cancer, you have to know what the incidence is likely to be in a population that you are studying so that you can determine if a treatment you are using is having an effect or not,” said Miller. “This measure will allow us to do that.” By offering women a much more precise idea of their actual risk, researchers and physicians hope to increase their use of mammography and monthly breast self-exams, as well as regular checkups by physicians.

The key to more effective treatment of breast cancer remains earlier detection, by self-examination for possible lumps and, even more effectively, by regular mammograms after age 40. But preliminary results of a study of 75 women at high risk of breast cancer found that the majority were not adept at doing self-exams.

The women were tested by Michael Stefanek, co-director of the breast surveillance service at Johns Hopkins Medical Institutions in Baltimore, in three areas: their general knowledge about how to do a self-exam, their ability to find lumps on models of a breast and their proficiency at doing a self-exam.

Despite knowing that they were at high risk for breast cancer, women on average in the study performed cursory exams that covered just half of each breast. They often missed the upper right quadrant of each breast, the area where 50% of breast tumors are found.