Breast Cancer Screening Concepts
Specificity and false-positive rate
The specificity of mammography is the likelihood of the test being normal when cancer is absent, whereas the false-positive rate is the likelihood of the test being abnormal when cancer is absent. If specificity is low, many false-positive examinations result in unnecessary follow-up examinations and procedures. (Refer to the subsection on Harms in the Screening With Mammography section of the Overview section of this summary for more information.)
Interval cancers are cancers that are diagnosed in the interval after a normal screening examination and before the subsequent screen. Some of these cancers were present at the time of mammography (false-negatives), and others grew rapidly in the interval between mammography and detection. As a general rule, interval cancers have characteristics of rapid growth [6,7] and are frequently of advanced stage at the time of discovery/diagnosis.
One study of 576 women with interval cancers reported that interval cancers are more prevalent in women aged 40 to 49 years. Interval cancers appearing within 12 months of a negative screening mammogram appear to be related to decreased mammographic sensitivity, attributable to greater breast density in 68% of cases. Those appearing within a 24-month interval appear to be related both to decreased mammographic sensitivity due to greater breast density in 37.6% and to rapid tumor growth in 30.6%.
Another study that compared the characteristics of 279 screen-detected cancers with those of 150 interval cancers found that interval cancers were much more likely to occur in women younger than 50 years and to be of mucinous or lobular histology; or to have high histologic grade, high proliferative activity, relatively benign features mammographically and/or to lack calcifications. Screen-detected cancers were more likely to have tubular histology; to be smaller, low stage, and hormone sensitive; and to have a major component of ductal carcinomain situ.
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Carney PA, Miglioretti DL, Yankaskas BC, et al.: Individual and combined effects of age, breast density, and hormone replacement therapy use on the accuracy of screening mammography. Ann Intern Med 138 (3): 168-75, 2003.
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.
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Buist DS, Porter PL, Lehman C, et al.: Factors contributing to mammography failure in women aged 40-49 years. J Natl Cancer Inst 96 (19): 1432-40, 2004.