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EPIDEMIOLOGY

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Incidence

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Breast cancer is the second most common cause of death for women and is the most common cause of death for women age 45 to 55. In 2015, it is estimated that 231,840 American women would be diagnosed with breast cancer and that 40,290 would die from this disease, making breast cancer the second most common cause of cancer-related morality in the United States, with lung cancer being the most common (1).

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In the early 1980s, the rates of breast cancer diagnosis rose sharply, likely related to increased mammographic screening, because it was the incidence of stage 0 and I carcinomas that rose most sharply. Data from the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute demonstrate that although the incidence of breast cancer has been stable since the late 1980s, there has been an increase in the percentage of breast cancers that are hormone receptor positive, which is thought to be due either changes in receptor assays or an increased use of hormone replacement therapy by women (2,3). The incidence of primary breast cancer then decreased around 2003, shortly after the publication of the Women’s Health Initiative (WHI) results, which prompted many healthy postmenopausal women to stop using hormone replacement therapy (4).

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Worldwide Trends

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Breast cancer incidence has long varied in different regions of the world. Incidence is highest in Northern Europe and North America and lowest in Asia and Africa. Data suggest that this variability is due not only to environmental factors but also to lifestyle. This is supported by the observation that breast cancer incidence is higher in second-generation Asian immigrants in the United States (5).

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Mortality

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Breast cancer overall mortality rates had been stable for more than 50 years prior to 1989. Starting in the 1990s, there has been a steady decrease in breast cancer deaths every year. Mortality rates declined by 1.4% per year from 1989 to 1995 and by 3.2% per year thereafter. This is thought to be due in part to increased use of mammography, resulting in earlier diagnosis, and the use of effective treatments. Mortality rates continue to be higher for African American women. This is due in part to disparities in health care access that exist both for diagnosis as well as treatment (6).

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RISK FACTORS

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Hereditary

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Family History
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Although it is known that family history is an important risk factor for breast cancer, only 25% of newly diagnosed patients have a positive family history. The Gail model was the first to incorporate the number of first-degree relatives into a comprehensive model of breast cancer risk assessment (7). Claus then assessed the estimated risk of breast cancer based ...

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