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The Canadian National Breast Screening Study (NBSS) is a randomized controlled trial to assess the effect of screening on breast cancer mortality. The NBSS designated a single reference radiologist who blindly reviewed over the course of the study 5200 randomly selected two-view mammographic examinations of women not known to have breast cancer. He also reviewed 575 screening-detected breast cancer (SBC) cases and 102 interval breast cancer (IBC) cases. All cancers were histologically proven. As a result of the reviews, comments on inter-observer agreement, interpretation, and technical quality were conveyed on an ongoing basis to radiologists appointed to 15 NBSS screening centers. Agreement of the reference radiologist with center radiologists was better for breast cancer cases (kappa = 0.511, P less than .002) than for those not known to have breast cancer (kappa = 0.307, P less than .002). Observer error and technical problems led to delayed detection in 22% of SBCs and 35% of IBCs. Another 11% of SBCs and 58% of IBCs were probably mammographically occult. No similarly comprehensive review of mammography during a screening program has been published. Suggestions arising from the NBSS review were sometimes resisted by center radiologists. Measures are suggested which might facilitate acceptance of recommendations arising from audit mechanisms in mammography screening programs, thereby enhancing opportunities for mammographic excellence.

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We report the sensitivity and specificity of first screen mammography in a 15-centre randomized screening trial. Of 44,718 women who received mammography and physical examination at first screening, 238 were diagnosed with breast cancer at first screen, 34 in the 12-month interval after the first screen, and 98 at the second screen. Seventeen of the interval cases and 47 of the second-year cancers were defined as potentially detectable at first screening. Interpretations of first screen mammograms by radiologists at the screening centres were matched to known histological outcomes. Simultaneous blind review of 2908 cases, which included all cancers detected at first and second screenings as well as interval cancers, was done by a single reference radiologist. The sensitivity of the technique as carried out at all NBSS centres was 0.75, the specificity 0.94, the positive predictive value 0.07, and the negative predictive value 0.998.

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Audit procedures for mammography interpretation in a national breast cancer screening program are described. Agreement between radiologists at five screening centers and a single reference radiologist was evaluated based on mammograms at initial screen in 739 women not known to have breast cancer and 204 breast cancer cases detected at or within a year of initial screen. Kappa statistics, used to measure agreement in the interpretation of mammograms between the reference and center radiologists beyond that attributable to chance, were 0.409 in women not known to have breast cancer, 0.472 in women with diagnosed breast cancer, and 0.493 for all women with p less than .0001 for all three categories. To our knowledge, this is the first report presenting measures of agreement made systematically, simultaneously, and on a continuing basis, during a screening program for quality assurance.

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Sensitivity and specificity of first screen mammography in a randomized screening trial at five centers are reported. A total of 23,101 women underwent mammography; in 139, breast cancer was detected at first screening; in 20, less than 12 months after first screening; and in 47, at second screening. All 206 cancer cases were histologically confirmed, and 174 were defined as being detectable at first screening. Average length of follow-up for all women was 3.2 years. Interpretations of first screen mammograms by the center radiologists were matched to known outcomes. Simultaneous blind review was performed by a single reference radiologist with mammograms from all 206 cancer cases and those of a random sample of 739 women not known to have breast cancer at 15 months or more after initial screening. Overall, the five screening centers achieved a sensitivity of 69% (range, 60%-78%), a specificity of 94% (range, 93%-96%), a positive predictive value of 8.6% (range, 3%-16%), and a negative predictive value of 99.7% (range, 99.6%-99.9%).

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The high incidence of breast cancer and its mortality make it imperative that women over 25 years of age have a clinical examination of their breasts at least every three years up to age 40 and annually thereafter. Before the age of 25, mammography is seldom indicated and then it should usually be limited to a spot film of a potential lesion. After 25, mammography is indicated for any woman with breast symptoms, women with metastases from cancer of an unknown primary site, and before any breast surgery. Women with a strong family history and those with large breasts should also have a mammogram between the ages of 25 and 35. Between the ages of 35 and 39 we recommend a baseline mammogram for asymptomatic women. After 39 and up to age 50, women should consult their physicians yearly to determine if, and how often, mammography should be performed. Finally, after age 50, annual mammography is suggested. In each of the above contexts, the radiologic examination should be coupled with clinical palpation of the breasts. A trained and experienced mammographer should recommend biopsy when mammograms show a typical spiculated mass; an ill-defined or even well defined mass that cannot be said to be benign; a suspicious distortion of local architecture; or a cluster of suspicious microcalcifications. Any cyst the nature of which is uncertain after puncture, or abnormal ducts on a galactogram also should make a biopsy mandatory. On the other hand, a normal mammogram should not prevent biopsy of a lesion of the nipple or of a lump detected clinically.(ABSTRACT TRUNCATED AT 250 WORDS)

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