Mammographic screening: no longer controversial.

A number of recent articles have made it abundantly clear that major reductions in breast cancer mortality can be achieved in both individuals and populations by routine screening mammography in women between the ages of 40 and 70. In randomized population trials comparing those invited and those not invited to mammographic screening, statistically significant reduction of breast cancer mortality ranges from 20 to 30%. However, even this statistically significant benefit is minimized by both contamination bias of the control group and compliance bias in the experimental group. The actual reduction in mortality is much understated for those women actually receiving mammography, by 50% or even more. Such a conclusion is borne out by the service screening reports from Sweden, the Netherlands, the United Kingdom, Finland, and from the state of Rhode Island. These communityand population-based reports result when all members of the population are invited, and demonstrates reductions in mortality of upwards of 60% in women who actually have mammography, and up to 50% reduction of all breast cancer deaths in entire populations that includes women who did not attend screening. In Florence, Italy, where breast screening began in the 1970s, there was an overall age-standardized mortality decrease of 41% in the entire population, 61% among patients from 45 to 54, and 45% for women from 65 to 74. In the entire state of Rhode Island, where 85% of women over 40 now receive a mammogram at least every 2 years, the highest rate in the United States, the overall population mortality decrease from breast cancer amounts to 25% since 1987, and is postulated to decrease by 50% over the next decade. These studies also indicate that the portions of the female population that did not participate in mammographic screening had essentially unchanged or only very minor improvements in mortality compared with previous years, despite widespread use of adjuvant systemic chemotherapy and hormonal therapy, particularly in young patients, patients over 70, or in patients with advanced disease. In Rhode Island, 73% of breast cancer deaths occurred in the 15 to 20% of patients who did not attend regular mammographic screening. This major breast cancer mortality reduction has resulted from a dramatic and statistically significant decrease in mean and median diameter of cancers, the proportion of cancers with lymph node metastases, the proportions of patients with 3 node metastases, and the proportion of patients with advanced stage (Stage 3, Stage 4), and higher-grade lesions. Interestingly, when comparing equivalent sizes and stages of breast cancers, it has been demonstrated that those cancers detected by mammography, in contrast to those discovered by clinical examinations, have a better long-term prognosis, even when lymph node metastases are present. The reason is that screen-detected cancers are smaller lesions within broad size categories (T1) or fewer metastatic nodes within broad nodal categories (N1; 1to 3-node metastases). These reports of reduced breast cancer mortality are based on mammographic screening intervals of up to 30 months, while the American experience encourages screening mammograms at yearly intervals, although the actual interval between screening mammograms may be close to 16 months rather than yearly. The potential impact of yearly screening, in contrast to the 2 to 2 and a half year screening interval commonly reported in Europe, holds the potential for still more substantiated