Screening by Mammography

Note: Separate PDQ summaries on Prevention of Breast Cancer; Breast Cancer Treatment; Male Breast Cancer Treatment; and Breast Cancer and Pregnancy Treatment are also available.

Screening by mammography, clinical breast examination, or both may decrease breast cancer mortality. The existence of benefit is uncertain due to the variable quality of the evidence and the inconsistency of results across studies. Any absolute benefit depends on the cancer incidence and the life expectancy of women being screened. Screening mammography detects noncancerous lesions as well as in situ and invasive breast lesions that are smaller than those detected by other means, and is associated with more diagnostic testing, surgeries, radiotherapy and anxiety. Some of these cancers would never become clinically significant so their diagnosis and treatment constitutes overdiagnosis and overtreatment. (Levels of evidence: 1,2,3,4,5) Screening mammography is more likely to miss cancers in women with radiographically dense breasts, as well as cancers that are rapidly growing. (Levels of evidence: 3,4,5)

Levels of Evidence

1: Evidence obtained from randomized controlled trials.

2: Evidence obtained from nonrandomized controlled trials.

3: Evidence obtained from cohort or case-controlled studies.

4: Evidence from ecologic and descriptive studies (e.g., international patterns studies, time series).

5: Opinions of respected authorities based on clinical experience, descriptive studies, or reports of expert committees.

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