Epidemiology

Incidence and Mortality

In 2000, an estimated 182,800 women were diagnosed with breast cancer in the United States. This figure represents approximately 30% of cancer diagnoses in women, with breast cancer ranking as the most frequently diagnosed cancer and the second leading cause of cancer death among women in the United States. The average American woman has a 12% lifetime risk of a personal breast cancer diagnosis. The longer a woman lives without cancer, the lower her future risk of breast cancer. For example, a 50-year-old woman who has not had breast cancer has an 11% chance of having breast cancer in her lifetime; a 70-year-old woman has a 7% chance of developing breast cancer during the remainder of her life. However, these risks can increase dramatically depending on an individual's personal and family history. Although breast cancer can affect younger women, it is most commonly seen in women in their middle to later years. In women under age 30, breast cancer is extremely uncommon. The annual incidence rises precipitously with each decade until age 50, then more gradually as a woman enters her sixth, seventh, and eight decades. Data from the surveillance, epidemiology, and end results (SEER) Program at the National Cancer Institute, a population-based data system consisting of nine separate state and local cancer registries that cover about 10% of the U.S. population, clearly demonstrate the relationship between age and incidence of breast cancer (Table 33.1).

Despite the estimate that a U.S. woman has a 1 in 8 chance of developing breast cancer in her lifetime, a woman only has a 3.4% risk of dying of breast cancer. The majority of women diagnosed with breast cancer will not die of the disease. Approximately 80% of women with breast cancer can expect to survive at least 5 years following diagnosis. The survival rate has been increasing in recent years, largely because of improvements in screening for early disease and the use of hormonal and cytotoxic treatments for early and advanced disease (Figure 33.1). There is no question that the use of adjuvant systemic therapy has made a real, although modest, impact on mortality as demonstrated by multiple randomized controlled trials. Despite an increasing incidence of breast cancer from the 1970s to 1997, the annual breast cancer mortality per 100,000 from 1987 to 1997 decreased by 19% among U.S. women aged 20 to 49, 18% for women aged 50 to 69, and 9% for women aged 70 to 79. In 1997, the annual breast cancer mortality rate per 100,000 U.S. women aged 70 to 79 was 112.5, compared to 10.8 and 65.0 among women aged 20 to 49 and 50 to 69, respectively.