Incidence and mortality
With an estimated 232,670 cases expected, breast cancer will be the most frequently diagnosed nonskin malignancy in U.S. women in 2014. Also in 2014, breast cancer will kill an estimated 40,000 women, second only to lung cancer as a cause of cancer mortality in women. Breast cancer also occurs in men, and it is estimated that 2,360 new cases will be diagnosed in 2014. Despite a prior long-term trend of gradually increasing breast cancer incidence in women, data from the Surveillance, Epidemiology, and End Results Program show a decrease in breast cancer mortality of 1.9% per year from 1998 to 2007.
The major risk factor for breast cancer is advancing age. A 30-year-old woman has a 1 in 250 chance of being diagnosed with breast cancer in the next 10 years, whereas a 70-year-old woman has a 1 in 27 chance.
Breast cancer incidence and mortality risk also vary on the basis of geography, culture, race, ethnicity, and socioeconomic status. Compared with other races, white women have a higher incidence of breast cancer that may be attributable, in part, to screening behavior.
Screening by mammography decreases breast cancer mortality by identifying cases for treatment at an earlier stage. However, screening also identifies more cases than would become symptomatic in a woman's lifetime, so screening increases breast cancer incidence. (Refer to the Overdiagnosis section in the PDQ summary on Breast Cancer Screening for more information.)
Etiology and pathogenesis of breast cancer
Breast cancer develops when a series of genetic mutations occurs. Initially, mutations do not change the histologic appearance of the tissue, but accumulated mutations will result in hyperplasia, dysplasia, carcinoma in situ, and eventually, invasive cancer. The longer a woman lives, the more somatic mutations occur and the more likely it is that these mutations will produce populations of cells that will evolve into malignancies. Estrogen and progestin cause growth and proliferation of breast cells that may work through growth factors such as transforming growth factor (TGF)-alpha. These hormones, whether endogenous or exogenous, may promote the development and proliferation of breast cancer cells.