Summary of Evidence
Screening by Mammography
Statement of benefit
Statement of harms
Screening by Clinical Breast Examination
Statement of benefits
Statement of harms
Screening by Breast Self-Examination
Statement of benefit
Statement of harms
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 MammographyStatement 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) [1] and three additional RCTs.[2-4]
- 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.[1] Absolute mortality benefit for women screened annually starting at age 40 years is 4 per 10,000 at 10.7 years.[5] 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.
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.[6] | 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.[7] | 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.[10] | 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.[4]
- External Validity: Poor.
Based on solid evidence, screening by clinical breast examination may lead to the following harms:
Table 2. Harms of Screening Clinical Breast Examination| Harms | Study Design | Internal Validity | Consistency | Magnitude of Effects | External Validity |
| Additional testing (false-positives) | Descriptive population-based | Good | Good | Specificity in women aged 50 to 59 years ranged between 88% and 99%.[13,14] | Good |
| False reassurance, delay in cancer diagnosis (false-negatives) | Descriptive population-based | Good | Fair | Of women with cancer, 17% to 43% had a negative clinical breast examination.[14] | Poor |
Screening by Breast Self-Examination
Statement of benefit
Based on fair evidence, teaching breast self-examination does not reduce breast cancer mortality.
Description of the Evidence
- Study Design: One RCT, case-control trials, and cohort evidence.
- Internal Validity: Good.
- Consistency: Fair.
- Magnitude of Effects on Health Outcomes: No difference in breast cancer mortality was seen after 10 years in Shanghai factory workers randomly assigned to receive breast self-examination instruction and reinforcement, compared with the control group. Forty percent of the women enrolled, however, were younger than 40 years.[15]
- External Validity: Poor.
Based on solid evidence, formal instruction and encouragement to perform breast self-examination leads to more breast biopsies and to the diagnosis of more benign breast lesions.
Description of the Evidence
- Study Design: One RCT.
- Internal Validity: Good.
- Consistency: Fair.
- Magnitude of Effects on Health Outcomes: Biopsy rate is 1.8% among the study population compared with 1.0% among the control group.[15]
- External Validity: Poor.
References
- Nyström L, Andersson I, Bjurstam N, et al.: Long-term effects of mammography screening: updated overview of the Swedish randomised trials. Lancet 359 (9310): 909-19, 2002. [PUBMED Abstract]
- Shapiro S: Periodic screening for breast cancer: the Health Insurance Plan project and its sequelae, 1963-1986. Baltimore, Md: Johns Hopkins University Press, 1988.
- Miller AB, To T, Baines CJ, et al.: The Canadian National Breast Screening Study-1: breast cancer mortality after 11 to 16 years of follow-up. A randomized screening trial of mammography in women age 40 to 49 years. Ann Intern Med 137 (5 Part 1): 305-12, 2002. [PUBMED Abstract]
- Miller AB, Baines CJ, To T, et al.: Canadian National Breast Screening Study: 2. Breast cancer detection and death rates among women aged 50 to 59 years. CMAJ 147 (10): 1477-88, 1992. [PUBMED Abstract]
- Moss SM, Cuckle H, Evans A, et al.: Effect of mammographic screening from age 40 years on breast cancer mortality at 10 years' follow-up: a randomised controlled trial. Lancet 368 (9552): 2053-60, 2006. [PUBMED Abstract]
- Zahl PH, Strand BH, Maehlen J: Incidence of breast cancer in Norway and Sweden during introduction of nationwide screening: prospective cohort study. BMJ 328 (7445): 921-4, 2004. [PUBMED Abstract]
- Elmore JG, Barton MB, Moceri VM, et al.: Ten-year risk of false positive screening mammograms and clinical breast examinations. N Engl J Med 338 (16): 1089-96, 1998. [PUBMED Abstract]
- Rosenberg RD, Hunt WC, Williamson MR, et al.: Effects of age, breast density, ethnicity, and estrogen replacement therapy on screening mammographic sensitivity and cancer stage at diagnosis: review of 183,134 screening mammograms in Albuquerque, New Mexico. Radiology 209 (2): 511-8, 1998. [PUBMED Abstract]
- Kerlikowske K, Grady D, Barclay J, et al.: Likelihood ratios for modern screening mammography. Risk of breast cancer based on age and mammographic interpretation. JAMA 276 (1): 39-43, 1996. [PUBMED Abstract]
- Porter PL, El-Bastawissi AY, Mandelson MT, et al.: Breast tumor characteristics as predictors of mammographic detection: comparison of interval- and screen-detected cancers. J Natl Cancer Inst 91 (23): 2020-8, 1999. [PUBMED Abstract]
- Ronckers CM, Erdmann CA, Land CE: Radiation and breast cancer: a review of current evidence. Breast Cancer Res 7 (1): 21-32, 2005. [PUBMED Abstract]
- Goss PE, Sierra S: Current perspectives on radiation-induced breast cancer. J Clin Oncol 16 (1): 338-47, 1998. [PUBMED Abstract]
- Fenton JJ, Rolnick SJ, Harris EL, et al.: Specificity of clinical breast examination in community practice. J Gen Intern Med 22 (3): 332-7, 2007. [PUBMED Abstract]
- Baines CJ, Miller AB, Bassett AA: Physical examination. Its role as a single screening modality in the Canadian National Breast Screening Study. Cancer 63 (9): 1816-22, 1989. [PUBMED Abstract]
- Thomas DB, Gao DL, Ray RM, et al.: Randomized trial of breast self-examination in Shanghai: final results. J Natl Cancer Inst 94 (19): 1445-57, 2002. [PUBMED Abstract]
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