Women carrying identified genetic alterations, such as those in BRCA1 or BRCA2, may make them more susceptible to breast cancer. About 5 percent of women with breast cancer have a hereditary form of this disease. Women with 75 percent or more dense breast tissue on a previous mammogram that made mammography reading difficult are at greater risk and are encouraged to have regular clinical breast exams. In addition, the incidence of breast cancer increases as a woman gets older. Breast cancer is uncommon in women under age 35.
Early detection is a means to detect breast cancer before the onset of symptoms.
High-quality mammography, with or without clinical breast exam, is the most effective technology presently available to detect breast tumors. However, like any test, mammography has some limitations. Several studies have shown that regular mammography screening can decrease a woman's chance of dying from breast cancer. In addition, early detection may prevent the necessity of removing lymph nodes, and in some cases may prevent the need for removing the entire breast or for undergoing chemotherapy. Evidence about whether regular mammography can decrease a woman's chance of dying from breast cancer has come from seven large-scale, randomized screening trials in which the proportion of women who died from breast cancer in the group assigned to screening is compared to those who were not offered screening.