Breast Cancer Screening

Epidemiology and Natural History

New invasive breast cancer was expected to affect 215,990 U.S. women in 2004; an additional 59,390 will have had in situ disease.22,23 One in 8.3 women will have breast cancer sometime in her lifetime, assuming she lives to age 85.24 The incidence of invasive breast cancer rises from about 43.5 in 100,000 among women aged under 40 to more than 468 in 100,000 among women aged over 75 years.25 Breast cancer incidence is lower among African-Americans than Caucasian-Americans (121.7 versus 140.8 in 100,000), but higher than in Asian-Americans (121.7 versus 97.2 in 100,000).26 An estimated 40,580 women in the United States will have died of breast cancer in 2004. Although the risk of death due to breast cancer for all races has decreased since the 1970s, African-Americans are more likely to die of breast cancer today than in 1969.26

An important factor in screening is the sojourn time, defined as the length of time from when a cancer can be found in humans by a particular technology to when it has grown enough to cause symptoms.27By contrast, lead time is the length of time between when a cancer is actually found by a screening test and when it would become symptomatic. Screening must occur at intervals that are the same or shorter than the sojourn time.

The heterogeneity of breast cancer biology poses challenges for screening. Although the estimated sojourn time for a breast cancer is about 2 years among women ages 40 to 49, it may be as long as 4 years among women ages 60 to 69.28,29 Although some ductal carcinoma in situ (DCIS) progresses to invasive disease, some does not,30 and much invasive cancer arises in the ducts and lobules of the breast without an in situ component being apparent.27 Investigators are evaluating whether biologic markers such as high- and low-grade nuclear changes, rather than morphology, would clarify whether some of what we call DCIS is actually a benign condition that does not need treatment.27 This important issue is at the heart of some people's concern about screening, because fully 16% of cancers found at screening in the United States are DCIS.31

Screening Tests

There are four tests commonly discussed for breast cancer screening: clinical breast examination, breast self-examination, film-screen mammography, and digital mammography. Table 24.1 summarizes the characteristics of these tests. Breast self-examination has been encouraged for years and consists of women systematically searching their own breasts in both supine and upright positions. Clinical breast examination is a similar systematic search by the healthcare provider.32

TABLE 24.1. Summary of screening test characteristics: breast cancer.
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