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Breast cancer is the most frequently diagnosed cancer in women, and it is estimated that there will be 212,920 new cases of invasive breast cancer and 61,980 new cases of in situ breast cancers among women in the United States in 2006 (16,379). Primarily due to increased utilization of screening mammography, breast cancer incidence rates increased rapidly in the 1980s. It is estimated that 41,430 breast cancer deaths will occur in 2006, with breast cancer ranking second among cancer deaths in women (after lung cancer). In contrast to the significant number of breast cancer cases in women, it is expected that 1,720 cases of breast cancer will be diagnosed in men in 2006, with approximately 460 breast cancer deaths in men. Due to a combination of early detection, increased awareness, and improvements in therapy, death rates from breast cancer actually declined by approximately 2.3% per year from 1990 to 2002 (379). The decrease in breast cancer mortality is demonstrated in Fig. 53.5.

There is considerable geographic, ethnic, and racial variability in breast cancer incidence. Ethnicity and national origin rank highly as predictors of risk for breast cancer with up to a 10-fold variation throughout the world (461). Compared to other well-established risk factors such as age of menarche and menopause, age at first childbirth, and family history, geographic and ethnic variability is quite significant. It is likely that a complex interaction of multiple factors, including genetic, environmental, and socioeconomic, contribute to the wide variability in age-adjusted incidence across populations.



The potential contribution of environmental factors and lifestyle is clearly demonstrated in the increasing incidence of breast cancers among Japanese American women and in trends of increasing incidence of breast cancer in Japan with recent changes in lifestyle. It is well recognized that the relatively low incidence of breast cancer in Asian immigrants to the United States has gradually increased as these immigrants have adapted to Western lifestyles (150). Rates of breast cancer over time in Japanese women in Los Angeles are now approaching the incidence in Caucasian women. In Japan, incidence rates have more than doubled from 1960 to 1990. This is likely a result of adaptation of Western lifestyles including fewer children, later marriage, increasing rates of obesity, and possibly dietary influences (112).
In the United States, the incidence of breast cancer in white women is higher than all other populations. Recent data from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program report incidence rates of 141 cases per 100,000 white women, compared to 122 in African American, 97 in Asian Pacific Islander, 90 in Hispanics, and 58 in American/Alaskan Natives (379).

Although incidence is lower in African American women, the age of onset is younger and African American women are more likely to be diagnosed at a more advanced stage. Several studies have reported an earlier onset of breast cancer in African American compared to white women by approximately 10 years. Furthermore, several studies have reported, after correcting for stage, that African American women have more aggressive biology and a poorer overall prognosis (62,385).