Mammography is the only imaging screening modality that has been studied by multiple randomized controlled trials. Across those trials, mammography has been shown to reduce deaths due to breast cancer. The randomized trials that show a benefit from mammography are those in which mammography increased detection of invasive breast cancers before they spread to lymph nodes . No randomized controlled trial has ever been performed on any other imaging screening modality and therefore there are no data showing that supplemental screening will or will not decrease mortality, though it is expected that other screening tests which increase detection of node-negative invasive breast cancers beyond mammography should further reduce breast cancer mortality.
Proving the mortality benefit of any supplemental screening modality would require a very large, very expensive randomized control trial with 15-20 years of follow-up. Given the speed of technological developments, any results would likely be obsolete by the trial’s conclusion. We do know that high-risk women having annual MRI screening are less likely to have advanced breast cancer than their counterparts who were not screened with MRI . We also know that average-risk women who are screened with ultrasound in addition to mammography are unlikely to have palpable cancer in the interval between screens [3, 4] with the rates of such “interval cancers” similar to women with fatty breasts screened only with mammography. The cancers found only on MRI or ultrasound are mostly small invasive cancers (average size of about 1 cm), and the vast majority are node negative [5, 6]; MRI also finds some DCIS. These results suggest there is a benefit to finding additional cancers with supplemental screening, though it is certainly possible that, like mammography, some of the cancers found with supplemental screening are slow growing and may never cause a woman harm, even if left untreated.