Summary of Evidence
Note: Separate PDQ summaries on Breast Cancer Prevention; Breast Cancer Treatment; Male Breast Cancer Treatment; and Breast Cancer Treatment and Pregnancy are also available.
Screening by Mammography
Statement of benefit
Based on fair evidence, screening mammography in women aged 40 to 70 years decreases breast cancer mortality. The benefit is higher for older women, in part because their breast cancer risk is higher.
Description of the Evidence
- Study Design: Meta-analysis of individual data from four randomized controlled trials (RCTs)  and three additional RCTs.[2,3,4]
- Internal Validity: Validity of RCTs varies from poor to good. Internal validity of meta-analysis is good.
- Consistency: Fair.
- Magnitude of Effects on Health Outcomes: Relative breast cancer-specific mortality is decreased by 15% for follow-up analysis and 20% for evaluation analysis. Absolute mortality benefit for women screened annually starting at age 40 years is 4 per 10,000 at 10.7 years. The comparable number for women screened annually starting at age 50 years is approximately 5 per 1,000. Absolute benefit is approximately 1% overall but depends on inherent breast cancer risk, which rises with age.
- External Validity: Good.
Statement of harms
Based on solid evidence, screening mammography may lead to the following harms:
Table 1. Harms of Screening Mammography
|Harm||Study Design||Internal Validity||Consistency||Magnitude of Effects||External Validity|
|Treatment of insignificant cancers (overdiagnosis, true positives) can result in breast deformity, lymphedema, thromboembolic events, new cancers, or chemotherapy-induced toxicities.||Descriptive population-based, autopsy series and series of mammary reduction specimens ||Good||Good||Approximately 33% of breast cancers detected by screening mammograms represent overdiagnosis.||Good|
|Additional testing (false-positives)||Descriptive population-based||Good||Good||Estimated to occur in 50% of women screened annually for 10 years, 25% of whom will have biopsies.||Good|
|False sense of security, delay in cancer diagnosis (false-negatives) ||Descriptive population-based ||Good||Good||6% to 46% of women with invasive cancer will have negative mammograms, especially if young, with dense breasts,[8,9] or with mucinous, lobular, or fast-growing cancers.||Good|
|Radiation-induced mutations can cause breast cancer, especially if exposed before age 30 years. Latency is more than 10 years, and the increased risk persists lifelong. ||Descriptive population-based ||Good||Good||Between 9.9 and 32 breast cancers per 10,000 women exposed to a cumulative dose of 1 Sv. Risk is higher for younger women.[11,12]||Good|
Screening by Clinical Breast Examination
Statement of benefits
Based on fair evidence, screening by clinical breast examination reduces breast cancer mortality.
Description of the Evidence
- Study Design: RCT, with inference.
- Internal Validity: Good.
- Consistency: Poor.
- Magnitude of Effects on Health Outcomes: Breast cancer mortality was the same for women aged 50 to 59 years undergoing screening clinical breast examinations with or without mammograms.
- External Validity: Poor.