New technologies in screening for breast cancer: a systematic review of their accuracy

Abstract

We systematically reviewed the literature on the accuracy of new technologies proposed for breast cancer screening. Four potential tests were identified (ultrasound, magnetic resonance imaging (MRI), full-field digital mammography (FFDM), and computer-aided detection (CAD)) for which primary studies met quality and applicability criteria and provided adequate data on test accuracy. These technologies have been assessed in cross-sectional studies of test accuracy where the new test is compared to mammography. Ultrasound, used as an adjunct to mammography in women with radiologically dense breasts, detects additional cancers and causes additional false positives. Magnetic resonance imaging may have a better sensitivity (but lower specificity) than mammography in selected high-risk women, but studies of this technology included small number of cancers. Computer-aided detection may enhance the sensitivity of mammography and warrants further evaluation in large prospective trials. One study of FFDM suggests that it may identify some cancers not identified on conventional mammography and may result in a lower recall rate. The evidence is currently insufficient to support the use of any of these new technologies in population screening, but would support further evaluation. British Journal of Cancer (2004) Despite recent controversy surrounding the efficacy of mammographic screening, it remains the only screening test for breast cancer that has been extensively evaluated in randomised controlled trials (RCTs) and shown to reduce breast cancer mortality (IARC, 2002;Nystrom et al, 2002). Since evidence exists that early detection reduces mortality from breast cancer, it is reasonable to evaluate a new screening test by assessing its effect on early detection of breast cancer. While RCTs examining mortality as an outcome are the gold standard, studies assessing new tests are commonly evaluated using surrogate measures as indicators of early breast cancer detection. These surrogate measures may be measurable at the time of screening or require follow-up. Immediate indicators include the cancer detection rate and the size, stage, and nodal status of cancers detected. The measure requiring follow-up is the interval cancer rate. Ascertainment of interval breast cancers poses a number of challenges that include identification (requiring linkage to cancer registries), standardisation, and validation of review and categorisation methods, as well as access to the films taken at diagnosis. Assessing whether tests differ in their interval cancer rate is best assessed by randomising people to the different tests. In designs in which women are assessed by both tests, women in whom cancers are detected by either test would obviously be identified and treated; interval cancers that arise thereafter would be those missed by both tests. To assess whether interval cancer rates differ between the tests is therefore best assessed by randomising women to the different tests. However, all of the immediately measurable surrogates can be asses...

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