Breast cancer incidence and mortality
Breast cancer is the most common noncutaneous cancer in U.S. women, with an estimated 64,640 cases of in situ disease, 232,340 new cases of invasive disease, and 39,620 deaths expected in 2013. Thus, fewer than 1 of 6 women diagnosed with breast cancer die of the disease. By comparison, about 72,220 American women are estimated to die of lung cancer in 2013. Males account for 1% of breast cancer cases and breast cancer deaths (refer to the Special Populations section of this summary for more information).
Widespread adoption of screening increases breast cancer incidence in a given population and changes the characteristics of cancers detected, with increased incidence of lower-risk cancers, premalignant lesions, and ductal carcinomain situ (DCIS). (Refer to the Ductal Carcinoma In Situ section in the Breast Cancer Diagnosis and Pathology section of this summary for more information.) Ecologic studies from the United States  and the United Kingdom  demonstrate an increase in DCIS and invasive breast cancer incidence since the 1970s, attributable to the widespread adoption of both postmenopausal hormone therapy and screening mammography. In the last decade, women have refrained from using postmenopausal hormones, and breast cancer incidence has declined, but not to the levels seen prior to the widespread use of screening mammography.
One might expect that if screening identifies cancers before they cause clinical symptoms, then the period of screening will be followed by a period of compensatory decline in cancer rates, either in annual population incidence rates or in incidence rates in older women. However, no compensatory drop in incidence rates has ever been seen following the adoption of screening, suggesting that screening leads to overdiagnosis—the identification of clinically insignificant cancers (refer to the Overdiagnosis section in the Harms of Screening Mammography section of this summary for more information).
Breast cancer incidence and mortality risk also vary according to geography, culture, race, ethnicity, and socioeconomic status (refer to the Special Populations section of this summary for more information).
Risk Factors for Breast Cancer
Breast cancer risk is affected by many factors besides participation in screening activities. Understanding and quantifying these risks is important to a woman, to her physicians, and to public policy makers.