Evidence of the effect of adjunct ultrasound screening in women with mammography-negative dense breasts: Interval breast cancers at 1 year follow-up

Surveillance of interval cancers (IC) provides a measure of breast screening efficacy. Increased breast density is a predictor of breast cancer risk and of the risk of IC in screening. Improving screening sensitivity in women with dense breasts, through adjunct ultrasound (US), may potentially reduce IC; however this has not been proven. We report on first-year IC in a retrospective cohort of 8865 women who had 19,728 screening examinations (2001–2006): women with non-dense (D1–D2) breasts received mammography (M) screening, and women with dense (D3–D4) breasts also received ultrasound. Data linkage with both hospital discharge records and cancer registry databases was used to identify IC.Underlying cancer rates (cancers observed within 1-year from screening) were 6.3/1000 screens in the D1–D2 group and 8.3/1000 screens in the D3–D4 group. Cancer detection rate (CDR) was 5.98/1000 in all screening examinations; in D3–D4 breasts ultrasound had an additional CDR of 4.4/1000 screens. There were 21 first-year IC, an overall interval cancer rate (ICR) of 1.07/1000 negative screens: 0.95/1000 in women <50 years and 1.16/1000 screens in women ⩾50 years. ICR by breast density were 1.0/1000 negative screens in D1–D2, and 1.1/1000 negative screens in D3-D4. Interval cancers were early stage (in situ or small invasive) cancers, almost all were node-negative. Screening sensitivity was 83.5% for mammography alone in D1–D2 breasts relative to 86.7% for mammography with ultrasound in D3–D4 breasts.Our study shows that including ultrasound as adjunct screening in women with D3–D4 breasts brings the IC rate to similar levels as IC in non-dense breasts – this suggests that additional cancer detection by ultrasound is likely to improve screening benefit in dense breasts, and supports the implementation of a randomised trial of adjunct ultrasound in women with increased breast tissue density.