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

References

6. 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]
   
   
7. 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]
   
   
8. 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]
   
   
9. 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]
   
   
10. 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]
    
    
11. 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]
    
    
12. Goss PE, Sierra S: Current perspectives on radiation-induced breast cancer. J Clin Oncol 16 (1): 338-47, 1998.  [PUBMED Abstract]