A new study estimates that the average 50-year-old woman has about a 1-in-18 chance of developing breast cancer in her next 20 years--half the risk implied by the oft-repeated statistic 1-in-9.

Many women overestimate their risk because of a faulty understanding of the numbers, which become more accurate when broken down by race and ethnicity. This study also suggests that projections over a shorter time period, 5 to 20 years, may be more meaningful than the lifetime risk statistic.

Lifetime risk is the likelihood that a newborn girl will develop breast cancer sometime during her entire life. The 1-in-9 statistic does not apply to women of all ages, explains Cyllene R. Morris DVM, PhD, of the Public Health Institutes California Cancer Registry in Sacramento, California.

Although breast cancer is much more common in older women than younger women, the risk of developing breast cancer during the remainder of an older womans life is actually lower than the risk for a newborn.

An older woman has already survived several decades free of breast cancer, while a newborn is still at risk of developing breast cancer (or dying of other causes) until she reaches that particular age, Morris says in the paper.

Several studies have shown that women generally overestimate their risk of developing breast cancer. Even women who are counseled or educated on breast cancer may still misinterpret the 1-in-9 statistic as a short-term probability rather than as the lifetime risk of a newborn girl.

Morris and colleagues at the California Department of Health Services compiled data from the registry on 109,165 women in the state diagnosed with breast cancer between 1993 and 1997.

The study will be published in the April issue of the American Journal of Preventive Medicine.

They found that, on average, a 50-year-old woman has a 1-in-86 risk of developing breast cancer in the next five
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Contact: Joel B. Finkelstein
jfinkelstein@cfah.org
202-387-2829
Center for the Advancement of Health
28-Mar-2001