Most breast cancers detected at screening ultrasonography were undetected at mammography, according to a study published in the February issue of Radiology.

Though mammography has proven to decrease breast cancer mortality, the tool loses its sensitivity in screening women with dense breasts. Additional screening with ultrasonography or MRI has been shown to be increasingly helpful for this demographic. Lead author Min Sun Bae, MD, of the Seoul Metropolitan Government Seoul National University in Korea, and colleagues retrospectively reviewed the mammograms of women with breast cancers to identify reasons for nondetection at mammography.

Five blinded radiologists reviewed mammograms of 329 women with 335 ultrasonography-depicted cancers to determine if the negative findings should be recalled. Three unblinded radiologists then re-reviewed the mammograms to determine the reasons for nondetection by using the reference location of the cancer on mammograms performed after ultrasonography or MRI. A comparison was then made between the number of cancers that were recalled by the blind radiologists and the reasons for nondetection distinguished by the unblinded radiologists.

Of the cancers involved in the study, 63 (19 percent) were recalled by three or more of the blinded radiologists. Moreover, 272 (81 percent) exhibited no mammographic findings that required immediate attention. During the unblinded review, 263 (78 percent) cancers were obscured by overlapping, dense breast tissues. Nine were not included in mammography because of difficult anatomic location or poor positioning. Sixty-three (19 percent) of the 335 lesions were interpretive errors, of which 52 were subtle findings and 11 were evident.

“Supplemental screening with US can depict mammographically occult or subtle cancers that would not be depicted at mammography alone in women with dense breast tissue,” wrote Bae and colleagues.