Incidence and Mortality

Breast cancer is the most common noncutaneous cancer in U.S. women, with an estimated 192,370 new cases of invasive disease (plus 62,280 cases of in situ disease) and 40,170 deaths in 2009.[1] Males account for 1% of breast cancer cases and breast cancer deaths (refer to the Special Populations section of this summary for more information).

Ecologic studies from the United States [2] and the United Kingdom [3] demonstrate an increase in breast cancer incidence during the last 3 decades, rising from 82 cases per 100,000 people in 1973 to 118 per 100,000 in 1998. Between 1970 and the early 1980s the increase was small and has been attributed to changes in reproductive behavior and hormone use. Since the mid-1980s, with the widespread adoption of screening mammography, the increase has been dramatic. By illustration, the incidence among British women aged 50 to 65 years nearly doubled between 1984 and 1994. Similarly, in Sweden, where more cancers are discovered in younger women, the incidence of breast cancer increased dramatically in counties that adopted screening.[4] Similar findings have been documented in the United States. Mammographic screening has also increased the diagnosis of noninvasive cancers and premalignant lesions. Whereas ductal carcinoma in situ was a rare condition before 1985, it is currently diagnosed in more than 55,000 American women per year (refer to the Ductal Carcinoma In Situ section of this summary for more information).

One might expect that screening will identify many cancers before they cause clinical symptoms, followed by a subsequent compensatory decline in cancer rates, seen either in annual population incidence rates or in incidence rates in older women. So far, no compensatory drop in incidence rates attributable to a change in screening patterns has been observed. This raises concerns about overdiagnosis-screening that identifies clinically insignificant cancers (refer to the Overdiagnosis section of this summary for more information).

The risk of breast cancer depends on age (see Table 3). The commonly cited lifetime risk of one in seven women is misleading because it expresses a cumulative lifetime risk, for more than 100 years. As seen in Table 3, the risk of an average 40-year-old woman developing breast cancer in the next 10 years is approximately 1.5% (less than 1 in 60). This statistic, however, includes 40-year-old women of all risk groups, without regard to their use of screening mammograms. Therefore, a 40-year-old woman without any risk factors will have a lower risk of being diagnosed with breast cancer. Her risk is lower if she recently had a normal mammogram, and it is lower if she forgoes mammography (because of overdiagnosis) (see below).

Table 3. Probability of Developing Invasive Breast Cancer Among Womena