Breast cancer is by far the most common cancer among women worldwide. In 2008, there were an estimated 1.29 million new cases. Public health data indicate that the global burden of breast cancer in women - measured by incidence, mortality, and economic cost - is substantial and on the increase.
Breast cancer screening is defined as the evaluation of a population of asymptomatic women who have no overt signs or symptoms of breast cancer, in an effort to detect unsuspected disease early, when treatment is more effective. Currently, the best screening method for detecting breast cancer is mammography, as documented in randomized controlled trials and according to a fulfillment of basic principles of screening: (1) earlier detection of disease will reduce mortality, (2) healthy individuals who are screened will not be harmed, and (3) the screening test must be widely available, well tolerated, and cost effective.
Since 1990, death rates associated with breast cancer in the United States have decreased steadily, with larger decreases seen in women <50 years of age (a decrease of 3.2% per year) than in those 50 years (2.0% per year). This decrease in breast cancer deaths has been attributed to both improved screening with mammography and improved therapy. Recently, the relative impact of screening versus improved therapy was evaluated in a meta-analysis, the results of which showed that the reduction in breast-cancer-associated mortality was affected more by screening than it was by therapeutic improvements. Screening with mammography has been proven to reduce breast cancer mortality rates by up to 44%; as a result, annual screening mammograms are now widely recommended for women older than 40 years of age.
This chapter reviews the randomized controlled trials of breast cancer screening with mammography, breast cancer screening programs, advantages versus disadvantages and controversies associated with screening mammography, and supplemental screening for breast cancer with ultrasound and breast MRI.