Most breast cancers are still detected by patients themselves, although the percentage of mammographically detected cancers has increased. Seventy-five to 80 percent of patients whose invasive cancers are detected by screening have negative axillary lymph nodes, which is associated with the best prognosis. For these reasons, breast cancer screening is now an important aspect of health care for all women 40 years of age and older.
Physical examination combined with mammography remains the standard method of assessing the breast.
In the evaluation of data from screening programs, it is necessary to distinguish between screening mammography and diagnostic mammography, because the incidence of breast cancer is higher in women referred for mammography because of breast complaints. Equipment now being used to perform mammography has greatly reduced radiation exposure during this procedure. Screening programs detect breast cancers in patients of all ages, but a reduction in mortality in women who have undergone screening has been established only for those between 50 and 69 years of age. The sensitivity of mammography has improved considerably since the time that many of the trials were performed that found no overall reduction in mortality for women younger than 50 years. Women who perform regular self-examination tend to have better prognoses if breast cancer develops.