Lifetime Risk of Breast Cancer
The lifetime risk of developing breast cancer is a commonly cited statistic. Many estimates of this figure have been derived using cancer rates for the total population. However, when explaining risk, we usually are referring to the cancer-free population rather than the total population. In 1993, collaborators from NCI, SEER registries, and the American Cancer Society published a revised method for calculating estimates of lifetime risk based on SEER data from 1975-1988. The data were adjusted so that the incidence reflected only first primary breast cancer; mortality included causes other than breast cancer. The population denominator for incidence was adjusted to reflect only women with no previous diagnosis of breast cancer. The calculations showed an overall lifetime risk for developing invasive breast cancer of one in eight women, derived from the 1987-88 data. In comparison with the figure for 1975-77 (1 in 10.6), the lifetime risk of developing breast cancer rose. Lifetime risk of dying of breast cancer remained generally flat. A large portion of the rise in risk of developing breast cancer may be attributed to early detection of prevalent cases due to increased use of mammography screening and lower mortality due to causes other than breast cancer (for example, coronary heart disease). In other words, more women are being screened for breast cancer, and they are dying less often of other causes. This study enabled researchers to develop an enhanced expression of the assessment of breast cancer risk as it relates to age and provided physicians with a more meaningful context in which to communicate this risk to their patients.
The interest in communicating risk led scientists at the NCI and the National Surgical Adjuvant Breast and Bowel Project (NSABP) to develop the Breast Cancer Risk Assessment Tool. This tool allows health professionals to project a woman's individualized estimate of risk for invasive breast cancer over a 5-year period and during her lifetime. The tool uses data from the Breast Cancer Detection and Demonstration Project, a mammography screening project involving over 280,000 women that was conducted in the 1970s. The Breast Cancer Risk Assessment Tool may be used by clinicians for clinical counseling purposes, such as recommending mammography at a younger age, or having more frequent clinical breast examinations, or providing reassurance to many women who had previously overestimated their risk of breast cancer.
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More information about breast cancer risk assessment can be found at http://www.cancer.gov/bcrisktool/