including women with a strong family history of breast or ovarian cancer and women who were treated for Hodgkin disease. There are several risk subgroups for which the available data are insufficient to recommend for or against screening, including women with a personal history of breast cancer, carcinoma in situ, atypical hyperplasia, and extremely dense breasts on mammography. Diagnostic uses of MRI were not considered to be within the scope of this review.

New evidence on breast Magnetic Resonance Imaging (MRI) screening has become available since the American Cancer Society (ACS) last issued guidelines for the early detection of breast cancer in 2003. A guideline panel has reviewed this evidence and developed new recommendations for women at different defined levels of risk. Screening MRI is recommended for women with an approximately 20-25% or greater lifetime risk of breast cancer,including women with a strong family history of breast or ovarian cancer and women who were treated for Hodgkin disease. There are several risk subgroups for which the available data are insufficient to recommend for or against screening, including women with a personal history of breast cancer, carcinoma in situ, atypical hyperplasia, and extremely dense breasts on mammography. Diagnostic uses of MRI were not considered to be within the scope of this review.

REAST CANCER SCREENING, ESpecially with mammography, has been recommended for many decades, 1 and the majority of women older than 40 years in the United States participate in screening activities. 2,3 Meanwhile, new screening modalities have been introduced, and some of these have been increasingly incorporated into community practice. However, none of the new technologies has been evaluated for its effect on breast cancer mortality. Community practice of screening may differ from the care provided within randomized clinical trials and is less often discussed in review articles. Reviews of breast cancer screening usually emphasize efficacy and results of randomized trials, particularly those involving screen-film mammography. 4-7 Efficacy of a screening tool is measured in experimental studies under ideal circumstances. 8 In contrast, effectiveness is defined as the extent to which a specific intervention "when deployed in the field in routine circumstances, does what it is intended to do for a specific population." 8 We systematically reviewed what is known about the community practice of mammography, clinical breast examination, and breast self-examination, when possible, comparing the results from community studies with CME available online at www.jama.com

MRI can detect cancer in the contralateral breast that is missed by mammography and clinical examination at the time of the initial breast-cancer diagnosis. (ClinicalTrials.gov number, NCT00058058 [ClinicalTrials.gov].).