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Breast cancer is the most common cancer among women both in the United States and in the world. It is the second leading cause of cancer death among women in the United States. Among U.S. women in 2009, approximately 192,370 new cases of invasive breast cancer and 62,280 carcinoma in situ will occur and 40,170 will die from breast cancer.1 In terms of its global burden, there are about 1.05 million new cases and 373,000 deaths each year worldwide.2

Incidence and Mortality

There is a 4- to 5-fold variation in breast cancer incidence rates worldwide, with the highest in North America (99.4/100,000) and the lowest in Asia (22.1/100,000) and Africa (23.4/100,000).3 However, mortality rates are relatively less variable, with Africa (16.2/100,000) being similar to North America (19.2/100,000). These international variations are partly due to differences in environmental and lifestyle factors, screening practices, and treatment strategies.

In the past 50 years, breast cancer incidence has increased worldwide, including in the United States, where the highest rate is found.4 Data from the Surveillance, Epidemiology, and End Results (SEER) program show that incidence increased in the 1980s and 1990s in the United States but decreased after 2002 mainly in white women4 (Fig. 4-1). During the same period, 5-year survival also increased, reaching 90% at year 1997 for women 50 years or older and 87% for women under 50 at diagnosis (Fig. 4-2).4 The continued improvement in prognosis may be attributable to both screening, which increases the diagnosis of small, localized breast tumors, and treatment effectiveness.

Figure 4-1

Trends in female breast cancer incidence and death rates by race and ethnicity, United States. Rates are age-adjusted to the 2000 U.S. standard population. (Data from Ries L, Melbert D, Krapcho M, et al. SEER Cancer Statistics Review, 1975-2005. Bethesda: National Cancer Institute; 2008.)

Figure 4-2

Breast cancer survival trends in the United States. Values shown are 5-year relative survival (survival adjusted for life expectancy—an approximation to breast cancer-specific survival). (Data from Ries L, Melbert D, Krapcho M, et al. SEER Cancer Statistics Review, 1975-2005. Bethesda: National Cancer Institute; 2008.)

Age at Onset

Breast cancer incidence rates increase with age, as shown by the log scale plot of age-specific cancer incidence rates in 5-year age groups (Fig. 4-3). For estrogen receptor (ER)-positive cancer, the incidence rates increase rapidly until approximately age 50 (proportional to the seventh power of the age), and then rise slowly (proportional to the first power of the age). However, the incidence rate of ER-negative cancer increases rapidly before age 50 (proportional to the fifth power of the age) and then remains constant. As a result, ER-positive tumors are more likely to occur ...

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