Ultrasound for breast cancer screening and staging.

The question then arises whether and for whom BWBS should be recommended. As yet there are no scientific criteria on which to base an answer, and the examination should not be considered the standard of care until its benefits can be established prospectively. We know that mass screening mammography will detect occult cancers in two to seven of every 1000 women screened, depending on patient age and whether the screens are prevalence or incidence examinations. Should we expect a similar yield for survey US? Kopans commented that Kolb's cancer detection rate was lower than would be expected from a mammographic prevalence screen. This was not a reasonable comparison. These women all had negative findings on screening mammography and would normally be told to have repeat screening mammography 1 year later. Kolb's cancer detection rate using US was comparable to a mammographic incidence screen, so the cancer diagnoses of these fortunate women were advanced by 1 year. To maximize the yield, it is obvious that US has little to offer over mammography in women with fatty breasts because mammography is less likely to be falsely negative. The group of patients in whom incidental cancers would be expected to be found more commonly are those with dense breasts who also are at higher-than-average risk either because of a previous personal history of breast cancer (Fig. 2) or a significant family history. Because it would be impractical to consider BWBS for all women with radiographically dense breasts, it would be useful to know what its potential yield would be in the relatively smaller group of high-risk patients. Annual mammography remains the standard of care for breast cancer screening. However, in our practice in Vancouver, I suggest that high-risk women undergo mammography and US annually, recognizing that this goes beyond the standard of care. Instead of having both examinations simultaneously, I recommend that they alternate the two modalities at 6-month intervals. Theoretically, this could increase lead-time in the detection of occult cancers. The usefulness of this approach remains to be determined. BWBS for staging in women known to have breast cancer has tremendous promise and should be considered for any breast cancer patient with dense breast tissue in whom the finding of additional unsuspected foci would change the planned management. The cost of implementation would be substantial but considerably less than staging MRI. A large-scale study comparing these two modalities is needed, including assessment of the impact of identifying additional mammographically occult lesions on breast cancer mortality.