Current Resources for Evidence-Based Practice, March/April 2018.

In November, 2009, the U.S. Preventive Services Task Force (USPSTF) updated recommendations for breast cancer screening. The new guidelines, based on updated review of the evidence, recommend against routine screening mammography for women aged 40-49 in the general population, call for biennial screening mammography in women aged 50-74, and state that the evidence is insufficient to recommend continued screening after age 75. These new recommendations have been the subject of heated debate, especially focused on the subset of women aged 40-49. This tutorial is intended to help readers better understand and communicate with women about the underlying scientific issues. Screening tests asymptomatic people at risk for a disease, with the goal of early detection, effective prevention or treatment, and improved outcomes. To be beneficial, screening for cancer must identify the disease earlier, and lead to treatment with better outcomes than treatment starting at the onset of disease symptoms without screening; benefits of screening must also outweigh harms of screening. Characteristics of both the test and the disease affect the value of a screening test. Test characteristics include sensitivity and specificity. Sensitivity is the ability of mammography to correctly identify those with the disease, while specificity is the ability of mammography to correctly rule out the disease in those who do not have it. Specificity is especially important in population-based breast cancer screening regimens because of significant harms, both physical and psychological, and costs, associated with follow-up for a positive screening test. Disease characteristics that affect screening performance include the prevalence of the condition and its natural history, i.e., whether and how fast it tends to progress, whether it may resolve spontaneously, and how it affects survival. These factors must be weighed against the potential harms of screening, which can include loss of perceived health, harms and costs of further testing to refute false positive test results, and harms and costs of overdiagnosis and pseudo-cure—unnecessary treatment because the disease