Purpose: We examined to what extent mammographic density affects screening performance when using full field digital mammography (FFDM).
Methods and Materials: We collected a consecutive series of 69,874 FFDM examinations (2003-2009) from one screening unit of the Dutch biennial screening program (50-75 years). Volumetric mammographic density was automatically assessed with Volpara version 1.5.0 (Matakina, New Zealand). Recall and breast cancer detection information was obtained from the screening registration system. Interval cancers were identified through linkage with the Netherlands Cancer Registry. Within four density categories, comparable to ACR breast density categories, we determined screening performance measures and linear trends with a Chi Square linear trend test.
Results: 19.7% of the examinations was categorised as density category 1 ('almost entirely fatty'), 43.1% as category 2, 29.4% as category 3 and 7.7% as category 4 ('extremely dense'). In total 421 screen-detected and 150 interval tumours were identified. Cancer detection rates were 3.7?, 6.4?, 6.6? and 6.3? in categories 1 to 4 respectively (p=0.005). Interval cancer rates increased with increasing density categories: 0.7?, 1.9?, 3.0? and 4.5?, respectively (p< 0.001). As a result, the sensitivity (proportion of screen-detected tumours of screen-detected and interval tumours) was lower in higher density categories: 85.0%, 77.6%, 69.0% and 58.6% respectively (p< 0.001). The number of false positives was higher in women with dense breasts: 11.4?, 14.1?, 18.3? and 28.6? for categories 1 to 4, respectively (p< 0.001).
Conclusion: Also when FFDM is used in breast cancer screening higher interval cancer and false-positive rates are observed in women with mammographically dense breasts.