third study reports the opposite—that fewer women who received false-positive results return for a screening mammogram within three years—but the difference between groups, although statistically significant was only 3 percent and of doubtful clinical relevance.66
In the event of a positive mammogram, a woman must undergo a secondary assessment phase involving needle and/or open surgical biopsy to establish a definitive diagnosis.c Exposure to unnecessary biopsies is a real danger. Biopsy rates for suspected cases of breast cancer vary considerably among countries, indicating that the technical limitations of mammography are only part of the reason for biopsies. The rates are influenced by multiple factors beyond screening, such as practice variation and risk assessment. For example, the physician must take into account not only a patient’s risk of breast cancer, but his or her confidence in the mammographic results (which can be influenced by patient characteristics such as breast density or previous surgeries), as well as risks associated with the health care system—such as the risk of malpractice suits. In principle, improved risk stratification should result in a lower rate of biopsies for benign conditions because there would be a smaller pool of low-risk women being screened. “Unnecessary” biopsies can also be reduced by the use of supplemental technologies.
High doses of radiation (0.2.5 to 20 Gy), such as those that occurred in the 1930s to 1950s due to atomic bomb radiation, multiple chest x-rays, and radiation treatment for breast disease, were associated with increased incidence of breast cancer in women below age 35 at exposure.29,59 However, radiation sensitivity among women drops precipitously after age 35,59 and although some caution may be warranted for regular mammographic screening of women below age 35,60 calculations indicate that radiation risk is extremely small compared with the benefits, even for women in their forties.28,29,48 Moreover, since the early days of mammography, image quality has improved markedly (Figure 2-1) and radiation exposure has been greatly reduced, so that the average amount of radiation absorbed during a mammogram is now very low.112 It is estimated that 100,000 women who were screened annually from ages 50 to 75 would lose about 13 years from