ASTOUND-2 is a large, prospective multicentre trial in Italy that directly compares the incremental cancer detection and “false positive” (false alarm) recall rates for ultrasound (sonogram) and tomosynthesis (a form of 3D mammography) in women with dense breasts after a negative standard (2D) mammogram. In 5,300 women with dense breasts, the additional screening tests found a total of 29 breast cancers missed by 2D mammography:

  •  3 were detected only by 3-D mammogram (tomosynthesis)
  • 14 were detected only by ultrasound
  • 12 were detected by both 3-D mammogram (tomosynthesis) and ultrasound

Based on the number of women screened, tomosynthesis detected an additional 2.8 breast cancers per 1,000 women screened. Ultrasound detected significantly more, at 4.9 breast cancers per 1,000 women screened and an additional 2.6 breast cancers per 1,000 women even after tomosynthesis (p=0.015). 

While additional screening with ultrasound detects more breast cancers than 3-D mammography, false positive rates are higher for ultrasound than for 3-D mammography in most studies, resulting in a greater number of women being called back for additional testing. In the ASTOUND study, the incremental false-positive recall rate was significantly higher for ultrasound (1.0%) compared to tomosynthesis (0.30%) (p < 0.001). 

Tagliafico AS, Mariscotti G, Valdosta F, et al.  A prospective comparative trial of adjunct screening with tomosynthesis or ultrasound in women with mammography-negative dense breasts (ASTOUND-2).  Eur J Cancer. 2018 Nov;104:39-46.