The False-Negative Mammogram
The false-negative mammogram -- a mammogram in which the cancer is visible but is not diagnosed by the radiologist -- remains a concern in screening programs. Efforts to overcome the false-negative mammogram might further improve the effectiveness of mammography. Dr. Jan Hendricks[4] reviewed the frequency and consequences of false-negative mammograms. In many large reports, false-negative mammograms constitute 17% to 30% of all interval cancers. Dr. Hendricks presented 3 representative experiences, as outlined in Table 5.
That is, of cancers diagnosed since the last "negative" screening test, half were new interval cancers, roughly one quarter were radiographically occult, and one quarter reflected previously "false-negative (FN)" mammograms. The single largest cause of false-negative mammograms is radiologist error. Strategies to ensure the availability of old mammograms, to have second radiologists review the study, and to minimize radiologist fatigue may all improve the efficacy of screening.
Another strategy for improving screening is to consider greater reliance on the clinical breast exam (CBE), performed by physicians, as opposed to the self-breast exam done by women on themselves. Dr. L. Bleyen,[5] of the European Group for Breast Cancer Screening and Gent University, reviewed published data on the effectiveness of the CBE. A CBE program has accompanied mammography in Gent since 1992. Women ages 40-69 years are screened every 2 years, and the CBE is conducted before the mammogram so that the examiner is not influenced by radiologic findings. A total of 33,132 screenings have been done. Cancers were found in 348 women; of these tumors, mammography alone detected 308 and CBE alone detected 206. Thus, 40 tumors (11.5 % of cases) would have been missed without CBE. The testing properties of CBE, mammography, and combined evaluation are shown in Table 6.
Furthermore, CBE detects cancers that share similar prognostic features with tumors detected by mammography. Thus, it is likely that CBE does detect clinically significant breast cancers. These findings are consistent with previous reports[6] showing that CBE can detect about 5% of tumors that would be missed on mammography, and that CBE has a positive predictive value of about 4% to 6%. Given the convenience of CBE, it should be part of the routine screening of women.
Another means for overcoming false-negative mammography might be the use of other radiologic measures for detecting tumors. Dr. G. Rizzatto[7] updated the role of ultrasound in screening patients for breast cancer. New techniques in ultrasound, including better assessment of vascular flow, have refined the ability of ultrasound to detect small tumors (less than 1 cm), to characterize multifocal disease, and to distinguish invasive from preinvasive cancers. The anticipated availability of better intravenous contrast agents may further enhance the ability of ultrasound in detecting cancers. However, at present, ultrasonography remains too time-consuming for practical use as a screening method, and its effectiveness as a screen for breast cancer has not been proven in clinical trials. Clearly, ultrasound will have a growing role in the evaluation of the clinically palpated or mammographically detected breast tumor.
© 2000 Medscape
Cite this: Highlights of the 2nd European Breast Cancer Conference - Medscape - Oct 23, 2000.
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