ABSTRACT
Approximately 1.4 million breast cancers are diagnosed annually on a worldwide basis, making it the most frequently diagnosed cancer in women. As shown in Figure 21.1, population-based cancer incidence rates are highest in Western, industrialized parts of the world such as North America and Europe, and lowest in low- and middle-income countries (LMICs). It is widely assumed that “Western” lifestyle and reproductive factors (such as delayed childbearing); postmenopausal hormone replacement therapy (very popular during the 1980s and 1990s as a strategy to minimize side effects of ovarian cessation); postmenopausal obesity; increased detection rates through screening mammography programs; and probably some as-yet poorly defined dietary and environmental factors account for the notably high incidence rates of high-income countries (HICs). In contrast, delayed diagnosis and limited treatment resources result in disproportionate mortality rates; approximately 60% of breast cancer deaths occur in LMICs, and as shown in Figure 21.1, breast cancer mortality-to-incidence ratios are more than 0.5 in LMICs but only 0.2–0.3 in industrialized nations.
